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 32.25%. Comparing base (c211214) to head (fe741b2).
⚠️ Report is 185 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (c211214) and HEAD (fe741b2). Click for more details.

HEAD has 4 uploads less than BASE

Flag	BASE (c211214)	HEAD (fe741b2)
	5	1

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #10645       +/-   ##
===========================================
- Coverage   86.11%   32.25%   -53.86%     
===========================================
  Files         496      510       +14     
  Lines       33655    36013     +2358     
===========================================
- Hits        28981    11617    -17364     
- Misses       4674    24396    +19722     

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