ci: Improve CI performance (no-changelog) (#7637)

1. Split backend and frontend tests to avoid them running in parallel
2. Enable coverage only on `master`

.github/workflows/units-tests-reusable.yml

@@ -18,11 +18,17 @@ on:
         required: false
         default: ''
         type: string
+      collectCoverage:
+        required: false
+        default: 'false'
+        type: string
 
 jobs:
   unit-test:
     name: Unit tests
     runs-on: ubuntu-latest
+    env:
+      COVERAGE_ENABLED: ${{ inputs.collectCoverage }}
     steps:
       - uses: actions/checkout@v3.5.3
         with:
@@ -51,10 +57,14 @@ jobs:
           path: ./packages/**/dist
           key: ${{ inputs.cacheKey }}
 
-      - name: Test
-        run: pnpm test
+      - name: Test Backend
+        run: pnpm test:backend
+
+      - name: Test Frontend
+        run: pnpm test:frontend
 
       - name: Upload coverage to Codecov
+        if: ${{ inputs.collectCoverage == 'true' }}
         uses: codecov/codecov-action@v3
         with:
           files: packages/@n8n/client-oauth2/coverage/cobertura-coverage.xml,packages/cli/coverage/cobertura-coverage.xml,packages/core/coverage/cobertura-coverage.xml,packages/design-system/coverage/cobertura-coverage.xml,packages/editor-ui/coverage/cobertura-coverage.xml,packages/nodes-base/coverage/cobertura-coverage.xml,packages/workflow/coverage/cobertura-coverage.xml