MySQL 5.7 introduced some optimizations to avoid file I/O during
ALGORITHM=INPLACE operations. While both innodb-index-online and
innodb-table-online will exercise both the merge sort files and
the online log files in 10.1, in 10.2 they would only exercise the
online log files.

Modify one test case in innodb.innodb-table-online so that
skip_pk_sort will not hold. In this way, this test case will
write and read the merge sort files. The other instrumented tests
in innodb-index-online and innodb-table-online will only write
and read online_log files.