Use getenv instead as $_ENV isn't reliable

Co-authored-by: Ryan McCue <[email protected]>

inc/composer/class-command.php

@@ -681,7 +681,7 @@ protected function is_linux() : bool {
 	 * @return boolean
 	 */
 	public static function is_wsl() : bool {
-		return ! empty( $_ENV['WSL_INTEROP'] );
+		return getenv( 'WSL_INTEROP' ) !== false;
 	}
 
 }