cicd: fix release when multiple branches track same tag

[korikuzma]

Our current approach can break when there are multiple branches that track the same tag:

$ echo $raw
origin/issue-380 origin/main origin/pypi-release-action origin/release origin/vcf-annotator-readme-update
$ branch=${raw##*/}
$ echo $branch
vcf-annotator-readme-update

@theferrit32 thanks for pointing out the multiple branches issue! I think this will fix the release action

[jsstevenson]

@korikuzma can you leave a brief (1 sentence apiece) description of the problem and the solution in the commit description when you squash? I think some of the innards of this github action can be a little opaque