General: Memoize the return value in wp_get_wp_version().

Cache the unmodified `$wp_version` value as a static. This retains the current behaviour during the upgrade process `$wp_version` referencing the version of WordPress being upgraded from.

Follow up to [58848].

Props Cybr, debarghyabanerjee, mukesh27, costdev, SergeyBiryukov, TobiasBg, desrosj, azaozz.
Fixes #61782.


git-svn-id: https://develop.svn.wordpress.org/trunk@59192 602fd350-edb4-49c9-b593-d223f7449a82

Author: peterwilsoncc

src/wp-includes/functions.php

@@ -8833,7 +8833,11 @@ function clean_dirsize_cache( $path ) {
  * @return string The current WordPress version.
  */
 function wp_get_wp_version() {
-	require ABSPATH . WPINC . '/version.php';
+	static $wp_version;
+
+	if ( ! isset( $wp_version ) ) {
+		require ABSPATH . WPINC . '/version.php';
+	}
 
 	return $wp_version;
 }