Fix coverage file path mismatch in CI workflow

[Copilot]

The Code Coverage Summary step failed because the test runner output path didn't match the expected path.

Test command produced: coverage/coverage/coverage.cobertura.xml
Workflow expected: coverage/coverage.cobertura.xml

The --coverage-output coverage.cobertura.xml parameter created an extra coverage/ subdirectory under --results-directory coverage.

Changes

• Changed coverage output filename from coverage.cobertura.xml to cobertura.xml
• Updated CodeCoverageSummary action to read from coverage/cobertura.xml

Final path is now coverage/cobertura.xml consistently.

Original prompt

Reference: https://github.com/exceptionless/Exceptionless/actions/runs/21479985333/job/61873539380

Figure out the RCA for this failure

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