Add GitHub action to delete checksum files whenever they're modified

[chelming]

This action runs whenever *checksum.txt is modified and pushed. It will delete the file, then add a commit for the deletion to the current branch.

Example run (note this will be cleaned up eventually):
https://github.com/chelming/Plants/actions/runs/11645400073

Commit history:
https://github.com/chelming/Plants/commits/test-modify-checksum?since=2024-11-02&until=2024-11-02

Example deletion commit:
chelming@ae0f157

[chelming]

I'm gonna close this but leave the branch in case it pops up again next year. So far, it seems like removing the files from the cache and adding the gitignore fixed it.

Steps for each checksum:
git rm -r --cached a474e7718792d510ab680f65dabb3508/checksum.txt