CI: Try creating build id

.github/workflows/client.yml

@@ -16,7 +16,28 @@ defaults:
     working-directory: app/client
 
 jobs:
+  build_id:
+    steps:
+      - name: 'Set build id'
+        id: build_id
+        # add a step output `steps.build_id.outputs.id` as the unique id
+        run: echo "::set-output name=id::$(date +%s)"
+      - name: 'Cache .build-id'
+        uses: actions/cache@v1
+        with:
+          # store the build id to github cache
+          path: ${{ github.workspace }}/.build-id
+          # use the build id to generate a completly unique cache
+          key: ${{ runner.os }}-build-id-${{ github.head_ref }}-${{ github.sha }}-${{ steps.build_id.outputs.id }}
+      - name: 'Save build id'
+        # store the build id to a folder that we can later cache.
+        run: |
+          mkdir -p .build-id
+          echo $BUILD_ID > .build-id/id
+        env:
+          BUILD_ID: ${{ steps.build_id.outputs.id }}
   build:
+    needs: build_id
     runs-on: ubuntu-latest
     defaults:
       run:
@@ -119,6 +140,21 @@ jobs:
       if: ${{ github.event_name == 'push' }}
       uses: actions/checkout@v2
 
+    # restore the build id
+    - name: 'Cache .build-id'
+      uses: actions/cache@v1
+      with:
+        path: ${{ github.workspace }}/.build-id
+        key: ${{ runner.os }}-build-id-${{ github.head_ref }}-${{ github.sha }}
+        restore-keys: |
+          ${{ runner.os }}-build-id-${{ github.head_ref }}-${{ github.sha }}
+    # set the build id from the restored cache
+    - name: 'Set build id'
+      id: build_id
+      run: echo "::set-output name=id::$(cat .build-id/id)"
+    # because of "record" and "parallel" parameters
+    # these containers will load balance all found tests among themselves
+
     - name: Use Node.js 10.16.3
       uses: actions/setup-node@v1
       with: