Fix release so we can only push to mvn central from main

.github/workflows/release.yml

@@ -6,12 +6,19 @@ on:
         description: "The branch to use to release from."
         required: true
         default: "main"
+
 jobs:
   release:
     name: Release to Maven Central
     runs-on: ubuntu-20.04
 
     steps:
+      - name: Check if branch is main
+        if: github.event.inputs.branch != 'main'
+        run: |
+          echo "This workflow can only run from the 'main' branch."
+          exit 1
+
       - name: Checkout source code
         uses: actions/checkout@v2
         with:
@@ -47,4 +54,4 @@ jobs:
           SONATYPE_USERNAME: ${{ secrets.SONATYPE_USERNAME }}
           DOCKERHUB_USERNAME: ${{ secrets.DOCKER_HUB_USERNAME }}
           DOCKERHUB_PASSWORD: ${{ secrets.DOCKER_HUB_PASSWORD }}
-          GPG_PASSPHRASE: ${{secrets.GPG_PRIVATE_KEY_PASSPHRASE}}
+          GPG_PASSPHRASE: ${{ secrets.GPG_PRIVATE_KEY_PASSPHRASE }}