Pin coverage reporter version in CI workflow

Set coverage-reporter-version to v0.6.15 in PR-test.yml to avoid a known 500 error bug in later versions.

Author: edeno

.github/workflows/PR-test.yml

@@ -91,6 +91,7 @@ jobs:
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           file: coverage.lcov
+          coverage-reporter-version: v0.6.15  # Pin to working version (v0.6.16+ has 500 error bug)
 
       # Execute example/tutorial notebooks to ensure they run end-to-end
       - name: Execute notebooks