workflow: don't check formatting

The workflow fails with the following error:

```
Run git diff origin/main...HEAD > changes.diff
fatal: ambiguous argument 'origin/main...HEAD': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'
Error: Process completed with exit code 128.
```