t3427: move the `filter-branch` invocation into the `setup` case

The step to prepare a pre-rebase commit history is _identical_ in _all_
of the test cases (except of course the `setup` case). It should
therefore clearly a part of the `setup` test case instead.

As the `git filter-branch` command is quite costly on platforms where
Unix shell scripting is simply slow (meaning: on Windows), this shaves
off a noticeable part of the runtime: in this developer's setup, the
time was reduced from ~1m25s to ~1m.

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

0 files changed, 0 insertions, 0 deletions