Build/Test Tools: Finalise changes to the WordPress versions used during upgrade testing from the development branch.

See #63170


git-svn-id: https://develop.svn.wordpress.org/trunk@60321 602fd350-edb4-49c9-b593-d223f7449a82

Author: johnbillion

.github/workflows/upgrade-develop-testing.yml

@@ -64,7 +64,7 @@ jobs:
         db-type: [ 'mysql' ]
         db-version: [ '5.7', '8.4' ]
         # WordPress 4.9 is the oldest version that supports PHP 7.2.
-        wp: [ '4.9', '6.5', '6.7', '6.8-RC1' ]
+        wp: [ '4.9', '6.6', '6.7', '6.8' ]
         multisite: [ false, true ]
 
         exclude: