codespaces: try codespaces system config if we can't get committer identity

[pmrowla]

workaround for #148

[codecov-commenter]

Codecov Report

Base: 82.23% // Head: 80.59% // Decreases project coverage by -1.64% ⚠️

Coverage data is based on head (64c13cc) compared to base (74b3a98).
Patch coverage: 8.33% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #149      +/-   ##
==========================================
- Coverage   82.23%   80.59%   -1.65%     
==========================================
  Files          25       25              
  Lines        3367     3401      +34     
  Branches      578      580       +2     
==========================================
- Hits         2769     2741      -28     
- Misses        517      568      +51     
- Partials       81       92      +11     

Impacted Files	Coverage Δ
src/scmrepo/git/backend/dulwich/__init__.py	78.76% <7.14%> (-2.65%)	⬇️
src/scmrepo/git/backend/pygit2.py	73.59% <9.09%> (-5.79%)	⬇️
src/scmrepo/utils.py	67.74% <0.00%> (-19.36%)	⬇️
tests/conftest.py	86.00% <0.00%> (-7.00%)	⬇️
src/scmrepo/asyn.py	96.55% <0.00%> (-3.45%)	⬇️
src/scmrepo/git/backend/gitpython.py	63.07% <0.00%> (-1.35%)	⬇️
src/scmrepo/git/__init__.py	83.72% <0.00%> (-0.34%)	⬇️

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