Add experimental VirusTotal scan

This step should automatically upload Gradle builds to VirusTotal and check for any false positives (like that one from McAfee we had a couple years ago).

...or it might just crash. We'll see.

.github/workflows/gradle.yml

@@ -33,3 +33,9 @@ jobs:
       uses: gradle/gradle-build-action@v2
     - name: Execute Gradle build
       run: ./gradlew build
+    - name: VirusTotal scan
+      uses: crazy-max/ghaction-virustotal@v4
+      with:
+        vt_api_key: ${{ secrets.VIRUSTOTAL_API_KEY }}
+        files: |
+          build/libs/.+jar$