Fix xmlconcat regression test

src/test/regress/expected/xml.out

@@ -56,9 +56,9 @@ SELECT xmlconcat('bad', '<syntax');
 ERROR:  invalid XML content
 DETAIL:  Expected '>'
 SELECT xmlconcat('<foo/>', NULL, '<?xml version="1.1" standalone="no"?><bar/>');
-                     xmlconcat                     
----------------------------------------------------
- <?xml version="1.1" standalone="no"?><foo/><bar/>
+             xmlconcat             
+-----------------------------------
+ <?xml version="1.1"?><foo/><bar/>
 (1 row)
 
 SELECT xmlelement(name element,