SQLStore: Fix wrong usage of xorm's insert functions in tests (#63850)

* SQLStore: Fix InsertId

* Prefs: Fix Insert return value

* Fix tests

* Add guidelines

pkg/infra/db/sqlbuilder_test.go

@@ -217,7 +217,8 @@ func createDummyUser(t *testing.T, sqlStore DB) *user.User {
 	err := sqlStore.WithDbSession(context.Background(), func(sess *Session) error {
 		sess.UseBool("is_admin")
 		var err error
-		id, err = sess.Insert(usr)
+		_, err = sess.Insert(usr)
+		id = usr.ID
 		return err
 	})
 	require.NoError(t, err)