Use nick-fields/retry action to work around intermittent ForgeGradle …

…asset download failures

.github/workflows/pr.yml

@@ -25,8 +25,14 @@ jobs:
           chmod +x gradlew
           ./gradlew build
 
+      # ForgeGradle datagen asset download often fails (see #692)
+      # so just allow it to automatically retry a few times
       - name: Run Datagen
-        run: ./gradlew runAllDatagen
+        uses: nick-fields/retry@v3
+        with:
+          timeout_minutes: 10
+          max_attempts: 3
+          command: ./gradlew runAllDatagen
 
       - name: Check Datagen
         run: |