Fix display of code changes in clang-format CI action

[tautschnig]

Versions of git-clang-format later than 11 issue exit code 1 when changes were made to the source code. Although our CI job ended with a non-zero exit code as expected, it terminated early than wanted so that the differences are not printed to the log.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.63%. Comparing base (32143dd) to head (daaed1d).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8609      +/-   ##
===========================================
+ Coverage    79.17%   79.63%   +0.45%     
===========================================
  Files         1733     1733              
  Lines       198963   197820    -1143     
  Branches     17967    18173     +206     
===========================================
  Hits        157536   157536              
+ Misses       41427    40284    -1143     

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