Fix calling base method in NpgsqlMigrationsSqlGenerator (#3443)

Fixes #3440

(cherry picked from commit 83f2cc3)

Author: roji

src/EFCore.PG/Migrations/NpgsqlMigrationsSqlGenerator.cs

@@ -184,8 +184,8 @@ protected override void Generate(
 
         using (builder.Indent())
         {
-            base.CreateTableColumns(operation, model, builder);
-            base.CreateTableConstraints(operation, model, builder);
+            CreateTableColumns(operation, model, builder);
+            CreateTableConstraints(operation, model, builder);
             builder.AppendLine();
         }