dev-cmd/bump-formula-pr: always use full git repo as tap remote

[dawidd6]

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Hi there folks!

I'm currently taking care of my GitHub Action action-homebrew-bump-formula and wanted to move my test formulae from separate repository to the same repository where the action is stored.
I've run into an issue, because the repository is not named properly (i.e. $USER/homebrew-$TAP), brew bump-formula-pr would try to access non-existent repository named for example dawidd6/tap, it depends how I cloned the tap of course. I've tracked it down to this changed line. Didn't test it on homebrew-core, but I think it should work the same as for my repository.

Steps to reproduce:

1. brew tap dawidd6/tap https://github.com/dawidd6/action-homebrew-bump-formula.git
2. brew bump-formula-pr --no-audit --no-browse --no-fork --version=0.1.12 --force dawidd6/tap/test-formula-url
3. Observe error "Not found".

[dawidd6]

So, I've blamed this line and found this PR #15082 😄.
Converting to draft for now, will find a solution working for both cases.

[MikeMcQuaid]

Thanks again @dawidd6!