Bugfix: Remove stashing in pre-commit script

[lenaploetzke]

Closes #2255

Describe your changes here:
Due to #2182, the pre-commit script uses stashing to run the pre-commit checks only on staged changes.
This can lead to strange and difficult-to-find Git behavior when merging branches.
For example, I had the case where the file .git/MERGE_HEAD was stashed but not reapplied afterwards.
It would be nice to find another solution for running only on staged changes, but the quick fix is to remove it.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.45%. Comparing base (c1a2993) to head (697c8b3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2254   +/-   ##
=======================================
  Coverage   78.45%   78.45%           
=======================================
  Files         115      115           
  Lines       19184    19184           
=======================================
  Hits        15050    15050           
  Misses       4134     4134           

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