tests: verify that `clone -c core.hooksPath=/dev/null` works again

tests: verify that `clone -c core.hooksPath=/dev/null` works again

As part of the protections added in Git v2.45.1 and friends,
repository-local `core.hooksPath` settings are no longer allowed, as a
defense-in-depth mechanism to prevent future Git vulnerabilities to
raise to critical level if those vulnerabilities inadvertently allow the
repository-local config to be written.

What the added protection did not anticipate is that such a
repository-local `core.hooksPath` can not only be used to point to
maliciously-placed scripts in the current worktree, but also to
_prevent_ hooks from being called altogether.

We just reverted the `core.hooksPath` protections, based on the Git
maintainer's recommendation in
https://lore.kernel.org/git/xmqq4jaxvm8z.fsf@gitster.g/ to address this
concern as well as related ones. Let's make sure that we won't regress
while trying to protect the clone operation further.

Reported-by: Brooke Kuhlmann <brooke@alchemists.io>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>