`on.<push|pull_request|pull_request_target>.<paths|paths-ignore>` should indicate how to match on git submodules

### Code of Conduct

- [x] I have read and agree to the GitHub Docs project's [Code of Conduct](https://github.com/github/docs/blob/main/.github/CODE_OF_CONDUCT.md)

### What article on docs.github.com is affected?

https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#onpushpull_requestpull_request_targetpathspaths-ignore

### What part(s) of the article would you like to see updated?

Add a note that for changes to files in git submodules, the path to the changed top level submodule should be used (instead of the path to files within the submodule).

### Additional information

It took a couple of attempts for a dev to figure out the correct way to make this work: https://github.com/PowerDNS/pdns/compare/56c6b1011d488e26673320b9d54aa4a3bce6a28d..a13665dcb8f9d57033820f53d83aa3e387ca9ecb