Add gcovr step to generate coverage report before Codecov upload

The codecov-action@v5 does not auto-process gcov data like the old bash
uploader did. This adds a step to run gcovr to convert .gcda/.gcno files
to Cobertura XML format, which codecov can parse.

Author: etr

.github/workflows/verify-build.yml

@@ -665,9 +665,15 @@ jobs:
          sleep 5 && ab -n 1000000 -c 100 127.0.0.1:8080/plaintext
       if: ${{ matrix.build-type == 'threads' }}
 
+    - name: Generate coverage report
+      run: |
+        cd build
+        gcovr --xml coverage.xml --xml-pretty
+      if: ${{ matrix.os-type == 'ubuntu' && matrix.c-compiler == 'gcc' && matrix.debug == 'debug' && matrix.coverage == 'coverage' && success() }}
+
     - name: Upload coverage to Codecov
       uses: codecov/codecov-action@v5
       with:
-        directory: build
+        files: build/coverage.xml
         fail_ci_if_error: false
       if: ${{ matrix.os-type == 'ubuntu' && matrix.c-compiler == 'gcc' && matrix.debug == 'debug' && matrix.coverage == 'coverage' && success() }}