Database: Ensure Non_unique index value is compared as a string in dbDelta().

Follow-up to [1575], [58994].

Props tsteel.
Fixes #64005.

git-svn-id: https://develop.svn.wordpress.org/trunk@60784 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-admin/includes/upgrade.php

@@ -3282,7 +3282,7 @@ function dbDelta( $queries = '', $execute = true ) { // phpcs:ignore WordPress.N
 					'fieldname' => $tableindex->Column_name,
 					'subpart'   => $tableindex->Sub_part,
 				);
-				$index_ary[ $keyname ]['unique']     = ( '0' === $tableindex->Non_unique ) ? true : false;
+				$index_ary[ $keyname ]['unique']     = ( '0' === (string) $tableindex->Non_unique ) ? true : false;
 				$index_ary[ $keyname ]['index_type'] = $tableindex->Index_type;
 			}