test: add null::text as default case expr

Author: swallowstalker

Diff for: internal/endtoend/testdata/json_traversal_as_select_expr_with_type_cast/postgresql/pgx/go/query.sql.go

@@ -16,6 +16,10 @@ FROM "mytable";
 SELECT CASE WHEN true THEN 'hello'::text ELSE null END
 FROM "mytable";
 
+-- name: GetNullable3B :many
+SELECT CASE WHEN true THEN 'hello'::text ELSE null::text END
+FROM "mytable";
+
 -- name: GetNullable4 :many
 SELECT CASE WHEN true THEN 'hello'::text END
 FROM "mytable";