onlineddl_vrepl suite: fix auto_increment flakyness

[shlomi-noach]

Description

This PR fixes a recurring CI error with onlineddl_vrepl_suite (not to be confused with another flakyness we have in onlineddl_vrepl). The flakyness fixed here has to do with AUTO_INCREMENT values, and which depends on the MySQL version. I simplified the tests by just saying something like "here's a starting point at auto_increment=8, gonna throw a bunch of stuff at the table, delete or whatnot, and expect resulting auto_increment to be two digit. That's it. Previously, we tried to hit the exact resulting value. But the value does not matter. What matters is that e.g. when rows are deleted, and table is duplicated, we don't fall back to auto_increment=8.

Related Issue(s)

#6926

Checklist

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[rohit-nayak-ps]

lgtm