Fix GitRepo.get_branch_commits_() to handle branch names conflicts with paths

[mih]

Specifically, conflicts of branch name with branch content.

Changelog

🐛 Bug Fixes

• GitRepo.get_branch_commits_() crashed when the given branch name also matched a file or directory in the active branch. Fixes wtf cannot handle worktrees with directories have the same name as any branch #6650

[codecov]

Codecov Report

Merging #6661 (b583f66) into maint (6dfb47f) will decrease coverage by 0.49%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            maint    #6661      +/-   ##
==========================================
- Coverage   91.17%   90.67%   -0.50%     
==========================================
  Files         353      353              
  Lines       44496    44498       +2     
==========================================
- Hits        40568    40348     -220     
- Misses       3928     4150     +222     

Impacted Files	Coverage Δ
datalad/support/gitrepo.py	90.82% <100.00%> (+<0.01%)	⬆️
datalad/support/tests/test_gitrepo.py	99.77% <100.00%> (+<0.01%)	⬆️
datalad/metadata/extractors/xmp.py	24.07% <0.00%> (-68.52%)	⬇️
datalad/metadata/extractors/tests/test_xmp.py	40.90% <0.00%> (-59.10%)	⬇️
datalad/metadata/tests/test_extract_metadata.py	54.05% <0.00%> (-45.95%)	⬇️
datalad/metadata/extract_metadata.py	69.44% <0.00%> (-30.56%)	⬇️
datalad/log.py	81.67% <0.00%> (-13.95%)	⬇️
datalad/cmd.py	83.07% <0.00%> (-11.03%)	⬇️
datalad/support/tests/test_sshconnector.py	91.97% <0.00%> (-6.80%)	⬇️
datalad/ui/progressbars.py	76.00% <0.00%> (-6.29%)	⬇️
... and 24 more

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[yarikoptic]

Looks LGTM. Travis - the same story with a tag as in another PR today

======================================================================
FAIL: datalad.tests.test_version.test__version__
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/dl-miniconda-1iv9f8d4/lib/python3.9/site-packages/nose/case.py", line 198, in runTest
    self.test(*self.arg)
  File "/home/travis/build/datalad/datalad/datalad/tests/test_version.py", line 61, in test__version__
    ok_startswith(__version__, changelog_version)
  File "/home/travis/build/datalad/datalad/datalad/tests/utils.py", line 451, in ok_startswith
    ok_(s.startswith(prefix),
AssertionError: String '0.16.1+29.g6f34f19' doesn't start with '0.16.2'

[github-actions]

🚀 PR was released in 0.16.3 🚀