Fix run condition (#18895)

Author: Kordyjan

.github/workflows/lts-backport.yaml

@@ -7,8 +7,7 @@ on:
 
 jobs:
   add-to-backporting-project:
-    if: "github.event.pull_request.merged == true
-         && !contains(github.event.push.message, '[Next only]')"
+    if: "!contains(github.event.push.message, '[Next only]')"
     runs-on: ubuntu-latest
 
     steps: