Build/Test Tools: Remove regular 6.2 & 6.3 branch performance testing.

Prior to WordPress 6.4, performance testing was performed using Puppeteer instead of Playwright (converted in [56926]). Because of the flaky nature of the workflow using Puppeteer, it was not converted to the reusable pattern implemented through #61213. It was instead removed from 6.2 and 6.3 in [58301] and [58330], respectively.

This removes the workflow for these branches from the strategy matrix when testing old branches to avoid errors and adds an expanded note about why those branches are missing.

See #61213, #61564.
Built from https://develop.svn.wordpress.org/trunk@58754


git-svn-id: http://core.svn.wordpress.org/trunk@58156 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.7-alpha-58753';
+$wp_version = '6.7-alpha-58754';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.