t0000: keep clean-up tests together

t0000: keep clean-up tests together

We check that test_when_finished cleans up after a test, and that it
runs even after a failure. Those two were originally adjacent, but got
split apart by the new test added in 477dcaddb6 (tests: do not let lazy
prereqs inside `test_expect_*` turn off tracing, 2020-03-26), and then
further by more lazy-prereq tests. Let's move them back together.

Signed-off-by: Jeff King <redacted>
Signed-off-by: Junio C Hamano <redacted>