* chore: Use `.yml` extension
Both of these files support the `.yml` extension. Normalize on that.
* fix: Add `.gitattributes` to ensure `LF` line-endings are committed
Avoids accidentally committing files with `CRLF` when they're created on Windows. Or worse, if some editors don't detect `LF` and would introduce mixed line-endings with `CRLF`.
Shouldn't be a problem in practice as we already have a linting check to catch this via CI during PRs. This file is complimentary, in that it should automate that concern away.
