Update PR validation workflow (modelcontextprotocol#177)

* Update PR validation workflow

* Update PR validation trigger configuration

* Add concurrency control to PR validation workflow

Author: devcrocod

.github/workflows/validate-pr.yml

@@ -3,7 +3,11 @@ name: Validate PR
 on:
   workflow_dispatch:
   pull_request:
-    types: [auto_merge_enabled]
+    branches: [main]
+
+concurrency:
+    group: ${{ github.workflow }}-${{ github.ref }}
+    cancel-in-progress: true
 
 jobs:
   validate-pr:
@@ -17,7 +21,7 @@ jobs:
           java-version: '21'
           distribution: 'temurin'
       - name: Setup Gradle
-        uses: gradle/actions/setup-gradle@ac638b010cf58a27ee6c972d7336334ccaf61c96 # v4.4.1
+        uses: gradle/actions/setup-gradle@v4
 
       - name: Clean Build with Gradle
         run: ./gradlew clean build