Fix cleanup script stack prefix for multi-attachment workflow

Update cleanup script calls to use '--stack-prefix thingpress-multi' instead
of 'thingpress-integration-test' to match the new stack naming convention.

This ensures cleanup script properly identifies and removes resources created
by the multi-attachment integration test workflow.

Affects both pre-deployment and final cleanup steps.

Author: rpcme

.github/workflows/integration-tests-multi.yml

@@ -67,7 +67,7 @@ jobs:
           echo "🧹 Pre-deployment cleanup of any existing test resources..."
           chmod +x scripts/cleanup-integration-test.sh
           ./scripts/cleanup-integration-test.sh \
-            --stack-prefix "thingpress-integration-test" \
+            --stack-prefix "thingpress-multi" \
             --no-dry-run \
             --region "${{ env.AWS_REGION }}" || true
         env:
@@ -164,7 +164,7 @@ jobs:
           
           # Run comprehensive cleanup to ensure no resources are left behind
           ./scripts/cleanup-integration-test.sh \
-            --stack-prefix "thingpress-integration-test" \
+            --stack-prefix "thingpress-multi" \
             --no-dry-run \
             --region "${{ env.AWS_REGION }}" || true