.github/workflows: publish test results for failed job

The GitHub Actions Linux Testing only reports limited information (can not see full stacktrace, time consumed, or stderr from child threads) when unit tests fail. Adding a step to upload the test report to Artifacts if the test fails. If the test is successful, no artifacts will be uploaded.

.github/workflows/testing.yml

@@ -53,6 +53,13 @@ jobs:
 
     - name: Build
       run: buildscripts/kokoro/unix.sh
+    - name: Post Failure Upload Test Reports to Artifacts
+      if: ${{ failure() }}
+      uses: actions/upload-artifact@v2
+      with:
+        name: Test Reports (JRE ${{ matrix.jre }})
+        path: ./*/build/reports/tests/**
+        retention-days: 14
     - name: Check for modified codegen
       run: test -z "$(git status --porcelain)" || (git status && echo Error Working directory is not clean. Forget to commit generated files? && false)