RTC: Fix undefined array_first() call in sync storage (WordPress#75869)

Co-authored-by: shekharnwagh <shekharnwagh@git.wordpress.org>
Co-authored-by: chriszarate <czarate@git.wordpress.org>

Author: 3 people

backport-changelog/7.0/10894.md

@@ -6,3 +6,4 @@ https://github.com/WordPress/wordpress-develop/pull/10894
 * https://github.com/WordPress/gutenberg/pull/75708
 * https://github.com/WordPress/gutenberg/pull/75711
 * https://github.com/WordPress/gutenberg/pull/75746
+* https://github.com/WordPress/gutenberg/pull/75869

lib/compat/wordpress-7.0/class-wp-sync-post-meta-storage.php

@@ -213,7 +213,13 @@ private function get_storage_post_id( string $room ): ?int {
 				)
 			);
 
-			$post_id = array_first( $posts );
+			/*
+			 * array_first() is a PHP 8.5 function. WordPress added
+			 * a polyfill in WP 6.9 (see https://core.trac.wordpress.org/ticket/63853).
+			 * Since Gutenberg must support the two most recent WordPress
+			 * versions (currently 6.8+), we cannot rely on it here.
+			 */
+			$post_id = $posts[0] ?? null;
 			if ( is_int( $post_id ) ) {
 				self::$storage_post_ids[ $room_hash ] = $post_id;
 				return $post_id;