ci(docs): scope pull_request triggers to integration branches (#5050)

Author: Mpdreamz

.github/workflows/docs-build.yml

@@ -1,6 +1,7 @@
 name: docs-build
 on:
   pull_request:
+    branches: [main]
     types: [opened, synchronize, reopened]
   push:
     branches: [main]

.github/workflows/docs-preview-cleanup.yml

@@ -1,6 +1,7 @@
 name: docs-preview-cleanup
 on:
   pull_request_target:
+    branches: [main]
     types: [closed]
 permissions:
   contents: none