Restore the 0.4.1 behavior for libcst.helpers.get_absolute_module

[lpetre]

Summary

I silently changed how this function behaved in #660

Anyone using this API and updating to 0.4.2 would experience different (and broken) behavior.

Test Plan

(libcstvenv) lpetre@lpetre-mbp LibCST % python -m unittest libcst.helpers.tests.test_module          
...............................................
----------------------------------------------------------------------
Ran 47 tests in 0.037s

OK

[codecov-commenter]

Codecov Report

Merging #684 (4f0d974) into main (460698a) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #684   +/-   ##
=======================================
  Coverage   94.81%   94.82%           
=======================================
  Files         246      246           
  Lines       25621    25653   +32     
=======================================
+ Hits        24293    24325   +32     
  Misses       1328     1328           

Impacted Files	Coverage Δ
libcst/helpers/__init__.py	100.00% <ø> (ø)
libcst/codemod/commands/remove_unused_imports.py	95.12% <100.00%> (ø)
libcst/codemod/visitors/_add_imports.py	95.45% <100.00%> (ø)
libcst/codemod/visitors/_gather_imports.py	96.15% <100.00%> (ø)
libcst/codemod/visitors/_imports.py	96.42% <100.00%> (ø)
libcst/codemod/visitors/_remove_imports.py	93.52% <100.00%> (ø)
libcst/helpers/module.py	100.00% <100.00%> (ø)
libcst/helpers/tests/test_module.py	100.00% <100.00%> (ø)

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[zsol]

looks good, thanks!