[BUGFIX] Isolate autoincrement tests

Tests regarding autoincrement handling should by isolated by resetting
autoincrement before invoking autoincrement code.

Resolves: #55115
Change-Id: I20727d04df708ce1f4d66acad4816f22ccc48a78
Reviewed-on: https://review.typo3.org/31220
Reviewed-by: Oliver Klee
Tested-by: Oliver Klee