[Backport maintenance/3.3.x] Fix source root not recognized

[github-actions]

Backport be53085 from #10036.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.80%. Comparing base (2287797) to head (bc37374).
Report is 163 commits behind head on maintenance/3.3.x.

Additional details and impacted files

@@                  Coverage Diff                  @@
##           maintenance/3.3.x   #10083      +/-   ##
=====================================================
- Coverage              95.85%   95.80%   -0.05%     
=====================================================
  Files                    174      174              
  Lines                  18873    18940      +67     
=====================================================
+ Hits                   18090    18146      +56     
- Misses                   783      794      +11     

Files with missing lines	Coverage Δ
pylint/lint/expand_modules.py	95.29% <100.00%> (ø)

... and 5 files with indirect coverage changes

[DanielNoord]

@Pierre-Sassoulas Let's merge? 😄

[Pierre-Sassoulas]

All right 😄 !