CMAKE_BUILD_PARALLEL_LEVEL for coverage

Author: anarthal

.github/workflows/coverage.yml

@@ -16,6 +16,7 @@ jobs:
       CXX: g++-11
       CXXFLAGS: -g -O0 -std=c++20 --coverage -fkeep-inline-functions -fkeep-static-functions
       LDFLAGS: --coverage
+      CMAKE_BUILD_PARALLEL_LEVEL: 4
     steps:
     - name: Checkout
       uses: actions/checkout@v3