t6000: use test_tick consistently

t6000: use test_tick consistently

The first two commits created in t6000 are done without test_tick,
meaning they use the current system clock. After that, we create one
with test_tick, which means it uses a deterministic time in the past.

The result of the "symleft flag bit is propagated down from tag" test
relies on the output order of commits from git-log, which in turn
depends on these timestamps. So this test is technically dependent on
the system clock time, though in practice it would only matter if your
system clock was set before test_tick's default time (which is in 2005).

However, let's use test_tick consistently for those early commits (and
update the expected output to match). This makes the test deterministic,
which is in turn easier to reason about and debug.

Note that there's also a fourth commit here, and it does not use
test_tick. It does have a deterministic timestamp because of the prior
use of test_tick in the script, but it will always be the same time as
the third commit. Let's use test_tick here, too, for consistency.  The
matching timestamps between the third and fourth commit are not an
important part of the test.

We could also use test_commit in all of these cases, as it runs
test_tick under the hood. But it would be awkward to do so, as these
tests diverge from the usual test_commit patterns (e.g., by creating
multiple files in a single commit).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>