tests: mark a couple more test cases as requiring `rebase -p`

tests: mark a couple more test cases as requiring `rebase -p`

The `--preserve-merges` option has been deprecated, and as a consequence
we started to mark test cases that require that option to be supported,
in preparation for removing that support eventually.

Since we marked those test cases, a couple more crept into the test
suite, and with this patch, we mark them, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>