Use 4 vCPUs for running coverage-recording tests

We changed the number of vCPUs for most scenarios in 55e5bdf, but
failed to also propagate this to coverage-recording test execution.

.github/workflows/coverage.yaml

@@ -46,7 +46,7 @@ jobs:
           echo "CCACHE_BASEDIR=$PWD" >> $GITHUB_ENV
           echo "CCACHE_DIR=$PWD/.ccache" >> $GITHUB_ENV
       - name: Configure CMake CBMC build with coverage instrumentation parameters
-        run: cmake -S . -Bbuild -Denable_coverage=1 -Dparallel_tests=2 -DCMAKE_CXX_COMPILER=/usr/bin/g++
+        run: cmake -S . -Bbuild -Denable_coverage=1 -Dparallel_tests=${{env.linux-vcpus}} -DCMAKE_CXX_COMPILER=/usr/bin/g++
       - name: Zero ccache stats and limit in size
         run: ccache -z --max-size=7G
       - name: Execute CMake CBMC build
@@ -98,7 +98,7 @@ jobs:
           echo "CCACHE_BASEDIR=$PWD" >> $GITHUB_ENV
           echo "CCACHE_DIR=$PWD/.ccache" >> $GITHUB_ENV
       - name: Configure CMake CBMC build with coverage instrumentation parameters
-        run: cmake -S . -Bbuild -Denable_coverage=1 -Dparallel_tests=2 -DCMAKE_CXX_COMPILER=/usr/bin/g++ -DCOVERAGE_CTEST_EXTRA_FLAGS="-E;^jbmc"
+        run: cmake -S . -Bbuild -Denable_coverage=1 -Dparallel_tests=${{env.linux-vcpus}} -DCMAKE_CXX_COMPILER=/usr/bin/g++ -DCOVERAGE_CTEST_EXTRA_FLAGS="-E;^jbmc"
       - name: Zero ccache stats and limit in size
         run: ccache -z --max-size=7G
       - name: Execute CMake CBMC build
@@ -161,7 +161,7 @@ jobs:
           echo "CCACHE_BASEDIR=$PWD" >> $GITHUB_ENV
           echo "CCACHE_DIR=$PWD/.ccache" >> $GITHUB_ENV
       - name: Configure CMake CBMC build with coverage instrumentation parameters
-        run: cmake -S . -Bbuild -Denable_coverage=1 -Dparallel_tests=2 -DCMAKE_CXX_COMPILER=/usr/bin/g++ -DCOVERAGE_CTEST_EXTRA_FLAGS="-R;^jbmc"
+        run: cmake -S . -Bbuild -Denable_coverage=1 -Dparallel_tests=${{env.linux-vcpus}} -DCMAKE_CXX_COMPILER=/usr/bin/g++ -DCOVERAGE_CTEST_EXTRA_FLAGS="-R;^jbmc"
       - name: Zero ccache stats and limit in size
         run: ccache -z --max-size=7G
       - name: Execute CMake CBMC build