Build/Test: Change default GitHub branch to trunk

See: https://make.wordpress.org/core/2021/11/10/default-git-branch-for-wordpress-wordpress-develop/
See: https://make.wordpress.org/core/2020/06/18/proposal-update-all-git-repositories-to-use-main-instead-of-master/

Fixes #54399



git-svn-id: https://develop.svn.wordpress.org/trunk@52130 602fd350-edb4-49c9-b593-d223f7449a82

.github/workflows/coding-standards.yml

@@ -5,7 +5,6 @@ on:
   # PHPCS checking was introduced in WordPress 5.1.
   push:
     branches:
-      - master
       - trunk
       - '3.[89]'
       - '[4-9].[0-9]'
@@ -14,7 +13,6 @@ on:
       - '[4-9].[0-9]*'
   pull_request:
     branches:
-      - master
       - trunk
       - '3.[89]'
       - '[4-9].[0-9]'
@@ -149,7 +147,7 @@ jobs:
 
   slack-notifications:
     name: Slack Notifications
-    uses: WordPress/wordpress-develop/.github/workflows/slack-notifications.yml@master
+    uses: WordPress/wordpress-develop/.github/workflows/slack-notifications.yml@trunk
     needs: [ phpcs, jshint ]
     if: ${{ github.repository == 'WordPress/wordpress-develop' && github.event_name != 'pull_request' && always() }}
     with: