Ported more features to GH Action

- Made the coverage report work for every job (based on the discussion with @TimvdLippe). Codecov merges all reports from a single CI invocation, giving us a more accurate coverage value.
- Added spotless invocation as a part of a single job (there is no point running spotless step for every job in the matrix - it will have the same results each time)

[skip travis]

.github/workflows/ci.yml

@@ -23,12 +23,15 @@ jobs:
       uses: actions/setup-java@v1
       with:
         java-version: ${{ matrix.java }}
+    - name: "Verify code formatting with Spotless. Run './gradlew spotlessApply' locally if this job fails."
+      #We want to run spotless check only in a single job
+      if: matrix.java == 11 && matrix.mock-maker == 'mock-maker-default'
+      run: ./gradlew spotlessCheck
     - name: Build on Java ${{ matrix.java }} with ${{ matrix.mock-maker }}
       run: ./gradlew build -m --scan # TODO: remove -m
       env:
         MOCK_MAKER: ${{ matrix.mock-maker }}
     - name: Upload coverage report
-      if: matrix.java == 8 && matrix.mock-maker == 'mock-maker-default'
       run: |
         ./gradlew coverageReport -s --scan && cp build/reports/jacoco/mockitoCoverage/mockitoCoverage.xml jacoco.xml || echo "Code coverage failed"
         bash <(curl -s https://codecov.io/bash) || echo "Codecov did not collect coverage reports"