Json test about max statement time fails with freebsd because on some
architectures the test might execute faster and the statement may not fail.
To simulate failure regardless of architecture, introduce a wait of seconds
longer than the max_statement_time.
Uses 500M+ of memory by repeating an 8 byte sequence 62.5M times.
Reduce the number of repeats on string reduced by 100 times.
Tested by applying against the reverted MDEV-24909 code. 1000 times
reduction was too much, but 100 still managed to trigger the bug.