fix parsing (.. union ..) union ..

Author: ea-rus

mindsdb_sql/parser/dialects/mindsdb/parser.py

@@ -1028,8 +1028,9 @@ def union(self, p):
 
     # tableau
     @_('LPAREN select RPAREN')
+    @_('LPAREN union RPAREN')
     def select(self, p):
-        return p.select
+        return p[1]
 
     # WITH
     @_('ctes select')