t/helper/test-fast-rebase.c: don't leak "struct strbuf"
Fix a memory leak that's been with us since
f9500261e0a (fast-rebase:
write conflict state to working tree, index, and HEAD, 2021-05-20)
changed this code to move these strbuf_release() into an if/else
block.
We'll also add to "reflog_msg" in the "else" arm of the "if" block
being modified here, and we'll append to "branch_msg" in both
cases. But after
f9500261e0a only the "if" block would free these two
"struct strbuf".
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>