Properly support "test with" for mu2e_trig_config

[kutschke]

Maybe this issue may require fixes in both this repo and Mu2e/codetools . I am not sure.

If you use the CI "test with" clause that includes a PR from mu2e_trig_config, it will work correctly but will generate an error message saying that there is no branch specified for the merge. It will then default to merging into HEAD, which is correct so long as we do not have other working branches in that repo. That is true for now but will not be in the medium term. For an example see:

Mu2e/Offline#1333 (comment)

The issue is to update the code in either CI and/or codetools to get the requested branch name and pass it to the section of codetools that uses it.