use gcovr instead of lcov in CI

- export coverage report as artifact

.gitlab-ci.yml

@@ -26,11 +26,12 @@ build-debian:
         - apt-get update && apt-get install -y cmake
         - apt-get update && apt-get install -y g++
         - apt-get update && apt-get install -y googletest
-        - apt-get update && apt-get install -y lcov
         - apt-get update && apt-get install -y libboost-program-options-dev
         - apt-get update && apt-get install -y libeigen3-dev
         - apt-get update && apt-get install -y ninja-build
         - apt-get update && apt-get install -y petsc-dev
+        - apt-get update && apt-get install -y python3 python3-pip
+        - pip3 install gcovr
         - >
             bash -c '
                 cd $(mktemp -d) &&
@@ -48,6 +49,8 @@ build-debian:
                 cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Debug -DCMAKE_CXX_FLAGS="--coverage" . &&
                 cmake --build build --target all &&
                 CTEST_OUTPUT_ON_FAILURE=1 cmake --build build --target test &&
-                lcov --capture --no-external --directory . --output-file lcov.info &&
-                lcov --list lcov.info
+                python3 -m gcovr --print-summary --sonarqube coverage.xml -j$(nproc) --root . build
             '
+    artifacts:
+        reports:
+            cobertura: coverage.xml