Build/Test Tools: Use a specific version of Gutenberg for E2E tests.

This updates the 6.4 branch to make use of the new `gutenberg-version` input introduced in [59220].

The past version of the plugin that supports WordPress 6.4 is `18.9.0`.

Props swissspidy.
See #61530.

git-svn-id: https://develop.svn.wordpress.org/branches/6.4@59221 602fd350-edb4-49c9-b593-d223f7449a82

Author: desrosj

.github/workflows/end-to-end-tests.yml

@@ -48,7 +48,7 @@ jobs:
         LOCAL_SCRIPT_DEBUG: [ true, false ]
     with:
       LOCAL_SCRIPT_DEBUG: ${{ matrix.LOCAL_SCRIPT_DEBUG }}
-      install-gutenberg: false
+      gutenberg-version: '18.9.0'
 
   slack-notifications:
     name: Slack Notifications