t5541: fix url scrubbing test when GPG is not set

t5541: fix url scrubbing test when GPG is not set

When the GPG prereq is not set, we do not run test 34. That
test changes the directory of the test script as a side
effect (something we usually frown on, but which matches the
style of the rest of this script). When test 35 (the
url-scrubbing test) runs, it expects to be in the directory
from test 34. If it's not, the test fails; we are in a
different sub-repo, our test-commit is built on a different
history, and the push becomes a non-fast-forward.

We can fix this by unconditionally moving to the directory
we expect (again, against our usual style but matching how
the rest of the script operates).

As an additional protection, let's also switch from "make a
new commit and push to master" to just "push to a new
branch". We don't care about the branch name; we just want
_some_ ref update to trigger the status output. Pushing to a
new branch is less likely to run into problems with
force-updates, changing the checked-out branch, etc.

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