title: Formatting Flutter codebase on GitLab CI in a merge request
body: <p>I can add the following <code>script:flutter format</code> to my CI yml file, and in the pipeline output I can see it finds files to format and does the formatting:</p>
  <pre><code>$ flutter format ./lib ./test
  Formatting directory ./lib:
  Formatted main.dart
  Formatting directory ./test:
  Unchanged widget_test.dart
  </code></pre>
  <p>But when it's finished I check the Pull Request, and the files are unchanged. How do I take the files that were formatting via my pipeline, and replace them in the pull request itself?</p>