Make new auto_explain test safe for log_error_verbosity = verbose.

Allow for the possible presence of a SQLSTATE code in the expected
warning message, similarly to b998196bb and 19408aae7 (although
here I see no need to allow more than one specific SQLSTATE).
Per gripe from Andrew Dunstan.

Discussion: https://postgr.es/m/c550ac53-5db5-3958-1798-50bae3d9af71@dunslane.net

contrib/auto_explain/t/001_auto_explain.pl

@@ -172,7 +172,7 @@ GRANT SET ON PARAMETER auto_explain.log_format TO regress_user1;
 
 	like(
 		$log_contents,
-		qr/WARNING:  permission denied to set parameter "auto_explain\.log_level"/,
+		qr/WARNING: ( 42501:)? permission denied to set parameter "auto_explain\.log_level"/,
 		"permission failure logged");
 
 }    # end queries run as regress_user1