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/ci-master.yml

@@ -48,7 +48,8 @@ jobs:
     with:
       ref: ${{ inputs.branch }}
       nodeVersion: ${{ matrix.node-version }}
-      cacheKey:  ${{ github.sha }}-base:${{ matrix.node-version }}-test-lint
+      cacheKey: ${{ github.sha }}-base:${{ matrix.node-version }}-test-lint
+      collectCoverage: true
 
   lint:
     name: Lint changes