Upgrade/Install: Update the $_old_files array for 6.6.

Props dd32, audrasjb, hellofromTonya.
Fixes #61665.

git-svn-id: https://develop.svn.wordpress.org/trunk@58744 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/update-core.php

@@ -765,6 +765,11 @@
 	'wp-admin/images/about-header-freedoms.svg',
 	'wp-admin/images/about-header-contribute.svg',
 	'wp-admin/images/about-header-background.svg',
+	// 6.6
+	'wp-includes/blocks/block/editor.css',
+	'wp-includes/blocks/block/editor.min.css',
+	'wp-includes/blocks/block/editor-rtl.css',
+	'wp-includes/blocks/block/editor-rtl.min.css',
 );
 
 /**