Fix isssue-closing script to work without project pages and default merge messages. (#289)

Fixes the issue-closing script in CAM-SIMA so that it will now
successfully close issues or PRs in the non-default branch when issues
are referenced in the PR message with a relevant keyword. This will
happen both without any attachment to a particular Github project, and
with any PR commit message.

Fixes #279 

Describe any changes made to build system: N/A

Describe any changes made to the namelist: N/A

List any changes to the defaults for the boundary datasets: N/A

Describe any substantial timing or memory changes: N/A

Code reviewed by: peverwhee, mwaxmonsky 

List all existing files that have been modified, old files eliminated,
new files added and describe the changes:

M .github/workflows/branch_push_workflow.yml
    - Update Github Action and Python versions.

M .github/scripts/branch_pr_issue_closer.py
- Update issue-closing script to work without projects or default PR
commit messages.

derecho/intel/aux_cam: All pass.
derecho/gnu/aux_cam:  All pass.

Summarize any changes to answers, i.e.,

what code configurations: N/A
what platforms/compilers: N/A
nature of change (roundoff; larger than roundoff but same climate; new
climate): N/A

Author: nusbaume