t7800: use single quotes for test bodies
In
eb84c8b6ce (git-difftool--helper: honor `--trust-exit-code` with
`--dir-diff`, 2024-02-20) we have started to loop around some of the
tests in t7800 so that they are reexecuted with slightly different
arguments. As part of that refactoring the quoting of test bodies was
changed from single quotes (') to double quotes (") so that the value of
the loop variable is accessible to the body.
As the test body is later on passed to eval this change was not required
though. Let's revert it back to use single quotes as usual in our tests.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>