Plugin tweaks: Check Jetpack version before enabling "blocks" module

In earlier versions, the file does not exist as a loadable module, which causes a PHP warning. WordCamp is pinned to an earlier version of Jetpack, so the warning appears. WordPress.org is a later version, which needs the module loaded.

mu-plugins/plugin-tweaks/jetpack.php

@@ -18,6 +18,9 @@
  * @return string[]
  */
 function available_jetpack_blocks( $modules, $min_version ) {
+	if ( ! defined( 'JETPACK__VERSION' ) || version_compare( JETPACK__VERSION, '13.8', '<=' ) ) {
+		return $modules;
+	}
 	if ( ! isset( $modules['blocks'] ) ) {
 		$modules['blocks'] = $min_version;
 	}