Run manifest ci check only when PR is labelled (#4568)

Signed-off-by: Sayali Gaikawad <gaiksaya@amazon.com>

Author: gaiksaya

.github/workflows/manifests.yml

@@ -1,15 +1,17 @@
 ---
-name: manifests
+name: manifests-ci-check
 
 on:
   pull_request:
-  paths:
-    - 'manifests/**/*.yml'
-    - '!manifests/templates/**/'
-    - 'legacy-manifests/**/*.yml'
+    types: [labeled]
+    paths:
+      - 'manifests/**/*.yml'
+      - '!manifests/templates/**/'
+      - 'legacy-manifests/**/*.yml'
 
 jobs:
   list-changed-manifests:
+    if: ${{ github.repository == 'opensearch-project/opensearch-build' && github.event.label.name == 'manifest-ci-check' }}
     runs-on: ubuntu-latest
     outputs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}