title: Use Gitlab's CI/CD with submodules - cannot run ssh
body: <p>I have a two private repositories: MyProject, MyProjetUtils.</p>
  <p>My project uses the MyProjectUtils as a submodule.</p>
  <p>My .gitsubmodules looks like this:</p>
  <pre><code>[submodule &quot;MyProjetUtils&quot;]
      path = MyProjetUtils
      url = git@gitlab.com:MyCompany/MyProjetUtils.git
  </code></pre>
  <p>My .gitlab-ci.yml file looks like this:</p>
  <pre><code>default:
    image: python:latest
  variables:
    GIT_SUBMODULE_STRATEGY: recursive
  all_test:
    stage: test
    script:
      - apt-get update
      - pip install -r requirements.txt
      - python tests/run_tests.py
  </code></pre>
  <p>The error I'm getting during the job run:</p>
  <pre><code>Updating/initializing submodules recursively with git depth set to 50...
  Submodule 'MyProjetUtils' (git@gitlab.com:MyCompany/MyProjetUtils.git) registered for path 'MyProjetUtils'
  Cloning into '/builds/MyCompany/MyProject/MyProjetUtils'...
  error: cannot run ssh: No such file or directory
  fatal: unable to fork
  fatal: clone of 'git@gitlab.com:MyCompany/MyProjetUtils.git' into submodule path '/builds/MyCompany/MyProject/MyProjetUtils' failed
  Failed to clone 'MyProjetUtils'. Retry scheduled
  </code></pre>
  <p>This error occur before the test stage. I've looked for answer <a href="https://docs.gitlab.com/ee/ci/git_submodules.html" rel="noreferrer">here</a>, and <a href="https://docs.gitlab.com/ee/ci/runners/configure_runners.html#git-submodule-strategy" rel="noreferrer">here</a> but could not find an answer.</p>