Remove duplicate Gradle workflows being triggered (#2541)

Author: sanderploegsma

.github/workflows/gradle.yml

@@ -1,9 +1,11 @@
-# This workflow will build a Java project with Gradle
-# For more information see: https://help.github.com/actions/language-and-framework-guides/building-and-testing-java-with-gradle
-
 name: Java CI with Gradle
 
-on: [push, pull_request, workflow_dispatch]
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
 
 defaults:
   run: