Build/Test Tools: Run automated testing workflows for trunk branch.

This ensures a seamless transition when the primary branch is changed from `master` to `trunk` in the GitHub mirror. Once the transition is completed, the `master` branch can be removed.

See https://make.wordpress.org/systems/2021/03/02/update-git-wordpress-org-to-rename-master-to-trunk/ and https://make.wordpress.org/core/2020/06/18/proposal-update-all-git-repositories-to-use-main-instead-of-master/.

See #52625.

git-svn-id: https://develop.svn.wordpress.org/trunk@50473 602fd350-edb4-49c9-b593-d223f7449a82

.github/workflows/javascript-tests.yml

@@ -5,6 +5,7 @@ on:
   push:
     branches:
       - master
+      - trunk
       - '3.[89]'
       - '[4-9].[0-9]'
     tags:
@@ -13,6 +14,7 @@ on:
   pull_request:
     branches:
       - master
+      - trunk
       - '3.[89]'
       - '[4-9].[0-9]'