Correct function_exists() check typo introduced in #33331. (#33513)

* Check for the correct function.

* add prefix

Co-authored-by: ntsekouras <ntsekouras@outlook.com>

lib/compat/wordpress-5.8/index.php

@@ -104,7 +104,7 @@ function build_query_vars_from_query_block( $block, $page ) {
 	}
 }
 
-if ( ! function_exists( 'gutenberg_register_legacy_query_loop_block' ) ) {
+if ( ! function_exists( 'gutenberg_render_legacy_query_loop_block' ) ) {
 	/**
 	 * Renders the legacy `core/query-loop` block on the server.
 	 * It triggers a developer warning and then calls the renamed
@@ -122,7 +122,7 @@ function gutenberg_render_legacy_query_loop_block( $attributes, $content, $block
 			sprintf( __( 'Block %1$s has been renamed to Post Template. %1$s will be supported until WordPress version 5.9.', 'gutenberg' ), $block->name ),
 			headers_sent() || WP_DEBUG ? E_USER_WARNING : E_USER_NOTICE
 		);
-		return render_block_core_post_template( $attributes, $content, $block );
+		return gutenberg_render_block_core_post_template( $attributes, $content, $block );
 	}
 }