Add merge queue for Java SDK (#129)

## Changes
Add merge queue for Java SDK to support merging PRs which haven't been
manually updated to latest main.

## Tests
<!-- How is this tested? -->

.github/workflows/push.yml

@@ -3,8 +3,8 @@ name: build
 on:
   pull_request:
     types: [opened, synchronize]
-  push:
-    branches: [main]
+  merge_group:
+    types: [checks_requested]
 
 jobs:
   fmt:
@@ -54,4 +54,4 @@ jobs:
           restore-keys: ${{ runner.os }}-m2
 
       - name: Check Unit Tests
-        run: mvn --errors test
+        run: mvn --errors test