Fix verify-staged-artifacts.yml to use proper SI 6.5.x branch

Author: artembilan

.github/workflows/verify-staged-artifacts.yml

@@ -31,6 +31,7 @@ jobs:
         with:
           repository: spring-projects/spring-integration
           show-progress: false
+          ref: 6.5.x
 
 
       - name: Set up Gradle