Increase the number of parallel jobs in Build workflow

Author: Growl1234

.github/workflows/build_test_cmake.yml

@@ -56,4 +56,4 @@ jobs:
           export CMAKE_PREFIX_PATH=${PEXSI32_ROOT}:${SUPERLU_DIST32_ROOT}:${PARMETIS32_ROOT}:${METIS32_ROOT}:${GKLIB_ROOT}:${CMAKE_PREFIX_PATH}
           rm -rf build
           cmake -B build ${{ matrix.build_args }}
-          cmake --build build -j2
+          cmake --build build -j 8