CI: Upload code coverage from rag tests

[JiwaniZakir]

Fixes #10644

RAG test coverage was not being reported to Codecov because .github/workflows/testing_rag.yml lacked an upload step after the test run. Adds the codecov/codecov-action@v5 step to testing_rag.yml, mirroring the pattern already used in _testing.yml.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 32.32%. Comparing base (c211214) to head (7aaf956).
⚠️ Report is 189 commits behind head on master.

❌ Your project status has failed because the head coverage (32.32%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

❗ There is a different number of reports uploaded between BASE (c211214) and HEAD (7aaf956). Click for more details.

HEAD has 4 uploads less than BASE

Flag	BASE (c211214)	HEAD (7aaf956)
	5	1

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #10645       +/-   ##
===========================================
- Coverage   86.11%   32.32%   -53.79%     
===========================================
  Files         496      510       +14     
  Lines       33655    36019     +2364     
===========================================
- Hits        28981    11643    -17338     
- Misses       4674    24376    +19702     

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