Support xcode-version-badge-markdown-file option

Action will no longer push to existing branch when there are no changes

I am currently maintaining numerous Swift Packages that don't receive a constant flow of updates, but do receive updates when new Swift updates come out, or as I think of useful additions.

To ensure that I can make some of these less frequent updates without too much friction and with confidence in their correctness I rely heavily on GitHub Actions, which I'll go over in this blog post.