Add dorny/test-reporter GitHub Actions plugin

The very first GitHub Actions run failed, but it was hard to see exactly
what went wrong. (I'm suspecting the Docker timeout needs to be bumped
up.) Hopefully this plugin helps provide more visibility into failures.

.github/workflows/run-tests.yaml

@@ -19,3 +19,14 @@ jobs:
 
       - name: Build and test
         run: ./gradlew build --no-daemon --warning-mode all
+
+      # Per the advice from:
+      # - https://octopus.com/blog/githubactions-running-unit-tests
+      - name: Post test report
+        uses: dorny/test-reporter@v1
+        if: always()
+        with:
+          name: Java tests
+          path: '**/build/test-results/test*/TEST-*.xml'
+          reporter: java-junit
+          fail-on-error: true