Tests: inserting an explicit value into a vers column

must behave as any other generated column: an error in the strict mode,
a warning otherwise.

mysql-test/suite/versioning/r/insert.result

@@ -308,8 +308,11 @@ create or replace table t1 (x int) with system versioning engine innodb;
 insert into t1 values  (1), (2);
 insert into t1 (row_start) select row_end from t1;
 ERROR HY000: The value specified for generated column 'row_start' in table 't1' ignored
+set sql_mode='';
 insert into t1 (row_start, row_end) values (DEFAULT, 1);
-ERROR HY000: The value specified for generated column 'row_end' in table 't1' ignored
+Warnings:
+Warning	1906	The value specified for generated column 'row_end' in table 't1' ignored
+set sql_mode=default;
 select @@sql_mode into @saved_mode;
 set sql_mode= '';
 insert into t1 (x, row_start, row_end) values (3, 4, 5);
@@ -322,6 +325,7 @@ select * from t1;
 x
 1
 2
+NULL
 3
 NULL
 # MDEV-14792 INSERT without column list into table with explicit versioning columns produces bad data

mysql-test/suite/versioning/t/insert.test

@@ -210,8 +210,9 @@ create or replace table t1 (x int) with system versioning engine innodb;
 insert into t1 values  (1), (2);
 --error ER_WARNING_NON_DEFAULT_VALUE_FOR_GENERATED_COLUMN
 insert into t1 (row_start) select row_end from t1;
---error ER_WARNING_NON_DEFAULT_VALUE_FOR_GENERATED_COLUMN
+set sql_mode='';
 insert into t1 (row_start, row_end) values (DEFAULT, 1);
+set sql_mode=default;
 select @@sql_mode into @saved_mode;
 set sql_mode= '';
 insert into t1 (x, row_start, row_end) values (3, 4, 5);