title: Symfony update fails with YAML errors
body: <p>I have a web application currently running on Symfony 4.3.5 without any problems.</p>
  
  <p>I call "php composer.phar update" in my project directory. Composer starts to download and upgrade packages to version 4.4 and finally fails with</p>
  
  <hr>
  
  <pre><code>Executing script cache:clear [KO]
   [KO]
  Script cache:clear returned with error code 1
  !!  
  !!  In FileLoader.php line 180:
  !!                                                                                 
  !!    The file "/home/markus/Programming/personal/config/packages/sonata_admin.ya  
  !!    ml" does not contain valid YAML: Unexpected characters near "                
  !!    - {                                                                          
  !!        route: app_workflows_erzeugemassnahmen_index,                            
  !!        label: "Fällige Massnahmen erstellen",                                   
  !!        roles: [ROLE_SUPER_ADMIN, ROLE_ADMIN_WORKFLOWS]                          
  !!      }" at line 76 (near "  }") in /home/markus/Programming/personal/config/pa  
  !!    ckages/sonata_admin.yaml (which is loaded in resource "/home/markus/Program  
  !!    ming/personal/config/packages/sonata_admin.yaml").                           
  !!                                                                                 
  </code></pre>
  
  <p>It complains about the same error in In YamlFileLoader.php line 693: and In Inline.php line 94:</p>
  
  <p>This "sonata_admin.yaml" file worked perfectly before. I use "yamllint" to check the file and it does not find anything wrong. I upload the file to online YAML checks and they don't find any problem. </p>
  
  <p>Interesting observations:
  - The message says that the error is in line 76 but the surrounding text shown is from line 48
  - When I empty the file completely, the upgrade fails with nearly the same error in a completely different file</p>
  
  <p>I use PHP 7.3 and most recent composer.
  Any ideas?</p>
  
  <p>Here is the config file:</p>
  
  <pre><code>---
  # Sonata Admin Bundle
  sonata_block:
    default_contexts: [cms]
    blocks:
      # enable the SonataAdminBundle block
      sonata.admin.block.admin_list: ~
      sonata.block.service.geburtstagsliste: ~
      sonata.block.service.vertragsliste: ~
      sonata.block.service.jubilare: ~
      sonata.block.service.konsistenzcheck: ~
      sonata.block.service.workflowstatistik: ~
      sonata.block.service.schulungsliste: ~
      # sonata.block.service.testblock: ~
  
  sonata_admin:
    persist_filters: true
    # for hide mosaic view button on all screen using `false`
    show_mosaic_button: false
    title: "Personal Admin"
    title_logo: "/bundles/sonatauser/default_avatar.png"
    security:
      handler: sonata.admin.security.handler.role
    dashboard:
      groups:
        Stammdaten Workflows:
          icon: '&lt;i class="glyphicon glyphicon-folder-close"&gt;&lt;/i&gt;'
          roles: [ROLE_ADMIN_STAMMDATEN, ROLE_SUPER_ADMIN]
        Stammdaten:
          icon: '&lt;i class="glyphicon glyphicon-folder-close"&gt;&lt;/i&gt;'
          roles: [ROLE_ADMIN_STAMMDATEN, ROLE_SUPER_ADMIN]
        Schulungen:
          icon: '&lt;i class="glyphicon glyphicon-folder-close"&gt;&lt;/i&gt;'
          label: ~
          label_catalogue: ~
          items:
            - {route: app_schulungsplanung_list, label: "Schulungsplanung"}
            - admin.schulungsevent
          roles: [ROLE_ADMIN_SCHULUNGSPLANUNG, ROLE_SUPER_ADMIN]
        Workflows/Massnahmen:
          icon: '&lt;i class="glyphicon glyphicon-folder-close"&gt;&lt;/i&gt;'
          items:
            - {
              route: app_workflows_ausstehendemassnahmen_index,
              label: "Übersicht Massnahmen",
            }
            - {
              route: app_workflows_erzeugemassnahmen_index,
              label: "Fällige Massnahmen erstellen",
              roles: [ROLE_SUPER_ADMIN, ROLE_ADMIN_WORKFLOWS],
            }
          roles: [ROLE_USER_WORKFLOWS, ROLE_SUPER_ADMIN, ROLE_ADMIN_WORKFLOWS]
        Workflows/Offboarding:
          icon: '&lt;i class="glyphicon glyphicon-folder-close"&gt;&lt;/i&gt;'
          items:
            - {
              route: app_workflows_ereignisuebersicht_index,
              label: "Übersicht Offboarding",
            }
            - {
              route: app_bewertungen_bewertungenuebersicht_index,
              label: "Übersicht Bewertungen",
            }
          roles: [ROLE_SUPER_ADMIN, ROLE_ADMIN_WORKFLOWS]
        Workflows/Bewertungen:
          icon: '&lt;i class="glyphicon glyphicon-folder-close"&gt;&lt;/i&gt;'
          items:
            - {
              route: app_bewertungen_bewertungenuebersicht_index,
              label: "Übersicht Bewertungen",
            }
          roles: [ROLE_USER_ZEUGNISSE]
        Workflows/Onboarding:
          icon: '&lt;i class="glyphicon glyphicon-folder-close"&gt;&lt;/i&gt;'
          items:
            - {
              route: app_workflows_ereignisuebersicht_onboardinguebersicht,
              label: "Übersicht Onboarding",
            }
            - {
              route: app_onboardingwizard_onboardingwizard_index,
              label: "Onboarding Wizard",
            }
          roles: [ROLE_SUPER_ADMIN, ROLE_ADMIN_WORKFLOWS]
      blocks:
        - {
          position: left,
          type: sonata.block.service.geburtstagsliste,
          roles: [ROLE_PERSONAL, ROLE_SUPER_ADMIN],
        }
        - {
          position: left,
          type: sonata.block.service.workflowstatistik,
          roles: [ROLE_ADMIN_WORKFLOWS, ROLE_SUPER_ADMIN],
        }
        - {
          position: right,
          type: sonata.block.service.vertragsliste,
          roles: [ROLE_PERSONAL, ROLE_SUPER_ADMIN],
        }
        - {
          position: right,
          type: sonata.block.service.schulungsliste,
          roles: [ROLE_PERSONAL, ROLE_SUPER_ADMIN],
        }
        - {
          position: right,
          type: sonata.block.service.konsistenzcheck,
          roles: [ROLE_PERSONAL, ROLE_SUPER_ADMIN],
        }
        - {
          position: left,
          type: sonata.block.service.jubilare,
          roles: [ROLE_PERSONAL, ROLE_SUPER_ADMIN],
        }
  </code></pre>