Drop the pin@ portion of the comment

So renovate can properly understand the digest, it would be nice to remove the unneeded pin@ characters.

The workaround for now is to use this instead

```
pin-github-action -c " {ref}" /path/to/workflow.yaml
```

- https://github.com/mheap/pin-github-action?tab=readme-ov-file#customising-the-ref-comment
- https://github.com/renovatebot/renovate/discussions/42451

Start at the pin-github-action entry point handling the -c option and compare its output with the custom ref comment documented in the README. The change is complete when the generated comment omits the pin@ portion while still providing the ref in a form Renovate can understand.

Written by the indexing model from the issue text.