[REVIEW] Fix pre-commit copyright check

[galipremsagar]

Description

This PR improves the copyright check script to handle cases where the ancestor branch-* does not have an upstream set.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[codecov]

Codecov Report

Base: 87.40% // Head: 87.48% // Increases project coverage by +0.07% 🎉

Coverage data is based on head (2e8630d) compared to base (f72c4ce).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-22.12   #11860      +/-   ##
================================================
+ Coverage         87.40%   87.48%   +0.07%     
================================================
  Files               133      133              
  Lines             21833    21866      +33     
================================================
+ Hits              19084    19129      +45     
+ Misses             2749     2737      -12     

Impacted Files	Coverage Δ
python/cudf/cudf/core/udf/__init__.py	50.00% <ø> (ø)
python/cudf/cudf/utils/ioutils.py	79.47% <ø> (ø)
...thon/dask_cudf/dask_cudf/tests/test_distributed.py	18.86% <ø> (+4.94%)	⬆️
python/cudf/cudf/__init__.py	90.69% <100.00%> (ø)
python/cudf/cudf/core/scalar.py	90.52% <100.00%> (+1.25%)	⬆️
python/dask_cudf/dask_cudf/sorting.py	93.29% <100.00%> (+2.11%)	⬆️
python/strings_udf/strings_udf/__init__.py	86.27% <100.00%> (-10.61%)	⬇️
python/cudf/cudf/io/text.py	91.66% <0.00%> (-8.34%)	⬇️
python/cudf/cudf/core/_base_index.py	82.20% <0.00%> (-3.35%)	⬇️
... and 6 more

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[bdice]

Tested offline with @galipremsagar.

[bdice]

@gpucibot merge

[galipremsagar]

@gpucibot merge