Show filenames of diff from auto-generated files in CI (#638)

There is a test in the CI that checks for differences between the
automatically generated files from OpenAPI. However, if this test fails,
it doesn't indicate which files have differences. I will modify the CI
to output this information.

Author: eucyt

.github/workflows/php-checks.yml

@@ -57,6 +57,8 @@ jobs:
       - if: ${{ env.DIFF_IS_EMPTY != 'true' && github.actor != 'renovate[bot]' }}
         run: |
           echo "There are changes from the auto-generated files by OAS. Please run diff-check.yml and merge the PR generated by it first."
+          echo "The files with differences are as follows."
+          echo "$(git --no-pager diff --name-only HEAD)"
           exit 1
   tests:
     name: Run checks on PHP ${{ matrix.php }}