nit: only prepare credentials on main branch

Author: notdryft

.github/workflows/build.yml

@@ -40,6 +40,7 @@ jobs:
           key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
 
       - name: Configure AWS credentials
+        if: github.ref == 'refs/heads/main'
         uses: aws-actions/configure-aws-credentials@v1
         with:
           aws-access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
@@ -48,6 +49,7 @@ jobs:
 
       - name: Login to Amazon ECR
         id: ecr-login
+        if: github.ref == 'refs/heads/main'
         uses: aws-actions/amazon-ecr-login@v1
 
       - name: Docker build