Work around gcov negative hit count bug in coverage report

gcov can produce negative branch hit values (gcc bug #68080). Newer
gcovr versions treat this as a fatal error. Adding
--gcov-ignore-parse-errors=negative_hits.warn_once_per_file lets the
coverage report complete while still logging the issue.

Author: etr

.github/workflows/verify-build.yml

@@ -742,7 +742,7 @@ jobs:
     - name: Generate coverage report
       run: |
         cd build
-        gcovr --root .. --filter '../src/' --xml coverage.xml --xml-pretty --print-summary
+        gcovr --root .. --filter '../src/' --xml coverage.xml --xml-pretty --print-summary --gcov-ignore-parse-errors=negative_hits.warn_once_per_file
       if: ${{ matrix.os-type == 'ubuntu' && matrix.c-compiler == 'gcc' && matrix.debug == 'debug' && matrix.coverage == 'coverage' && success() }}
 
     - name: Upload coverage to Codecov