Upgrade/Install: Skip preloading Requests for WordPress versions before 4.6.

Skip preloading Requests files in `_preload_old_requests_classes_and_interfaces()` when updating from a WordPress version older than 4.6.

Why?

Requests library was first introduced into WordPress 4.6 via #33055 / [37428]. If a user is upgrading from a version older than 4.6, this changeset prevents the Requests preloading to prevent a fatal error of attempting to load files that do not exist in their current WordPress version.

Follow-up to [54997], [37428].

Props afragen, costdev, ironprogrammer, antonvlasenko.
Fixes #57662.

git-svn-id: https://develop.svn.wordpress.org/trunk@55296 602fd350-edb4-49c9-b593-d223f7449a82

Author: hellofromtonya

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

@@ -1595,11 +1595,22 @@ function update_core( $from, $to ) {
  *
  * @global array              $_old_requests_files Requests files to be preloaded.
  * @global WP_Filesystem_Base $wp_filesystem       WordPress filesystem subclass.
+ * @global string             $wp_version          The WordPress version string.
  *
  * @param string $to Path to old WordPress installation.
  */
 function _preload_old_requests_classes_and_interfaces( $to ) {
-	global $_old_requests_files, $wp_filesystem;
+	global $_old_requests_files, $wp_filesystem, $wp_version;
+
+	/*
+	 * Requests was introduced in WordPress 4.6.
+	 *
+	 * Skip preloading if the website was previously using
+	 * an earlier version of WordPress.
+	 */
+	if ( version_compare( $wp_version, '4.6', '<' ) ) {
+		return;
+	}
 
 	if ( ! defined( 'REQUESTS_SILENCE_PSR0_DEPRECATIONS' ) ) {
 		define( 'REQUESTS_SILENCE_PSR0_DEPRECATIONS', true );