[github-actions] fix coverage reporting in unit workflow (#8737)

.github/workflows/unit.yml

@@ -63,6 +63,8 @@ jobs:
 
   unit-tests:
     runs-on: ubuntu-20.04
+    env:
+      COVERAGE: 1
     steps:
     - name: Harden Runner
       uses: step-security/harden-runner@18bf8ad2ca49c14cbb28b91346d626ccfb00c518 # v2.1.0
@@ -75,7 +77,7 @@ jobs:
     - name: Bootstrap
       run: |
         sudo rm /etc/apt/sources.list.d/* && sudo apt-get update
-        sudo apt-get --no-install-recommends install -y ninja-build
+        sudo apt-get --no-install-recommends install -y ninja-build lcov
     - name: Build Simulation
       run: ./script/cmake-build simulation
     - name: Test Simulation
@@ -84,10 +86,17 @@ jobs:
       run: ./script/cmake-build posix
     - name: Test POSIX
       run: cd build/posix && ninja test
+    - name: Generate Coverage
+      run: |
+        ./script/test generate_coverage gcc
+    - uses: actions/upload-artifact@83fd05a356d7e2593de66fc9913b3002723633cb # v3.1.1
+      with:
+        name: cov-unit-tests
+        path: tmp/coverage.info
+
 
   upload-coverage:
-    needs:
-    - unittests
+    needs: unit-tests
     runs-on: ubuntu-20.04
     steps:
     - name: Harden Runner