I think this is a formatting error/quirk. If I write it

      run: |
        sh -c "
        (git diff --quiet HEAD^ VERSION && git diff --quiet HEAD^ src/**) || \
          ! git diff --quiet HEAD^ src/VERSION
        "

it works.

I think this is a formatting error/quirk. If I add a new line before the command, with the | syntax, as

      run: |
        sh -c "
        (git diff --quiet HEAD^ VERSION && git diff --quiet HEAD^ src/**) || \
          ! git diff --quiet HEAD^ src/VERSION
        "

it works.