jailsetup.sh: ensure safe.directory=* when running git

jailsetup.sh: ensure safe.directory=* when running git

With this announcement:

    https://lore.kernel.org/git/xmqqv8veb5i6.fsf@gitster.g/
    "[ANNOUNCE] Git v2.35.2 and below for CVE-2022-24765"
    Date: Tue, 12 Apr 2022 10:01:21 -0700

Git versions 2.30.3, 2.31.2, 2.32.1, 2.33.2, 2.34.2 and 2.35.2 were
released on 2022-04-12 and immediately broke uses of the per-project
config setting "core.sharedrepository" when set to a non-false value.

Girocco cannot function without "core.sharedrepository" set to a
non-false value.

The following day with this announcement:

    https://lore.kernel.org/git/xmqq1qy04iqa.fsf@gitster.g/
    "[ANNOUNCE] Git v2.35.3 and below as a usability fix"
    Date: Wed, 13 Apr 2022 17:22:05 -0700

Git versions 2.30.4, 2.31.3, 2.32.2, 2.33.3, 2.34.3 and 2.35.3 were
released on 2022-04-13 providing a means to "opt-out" of the breakage
that effectively disabled use of "core.sharedrepository" set to a
non-false value.

Later versions of Git (including the since released version 2.36.0)
also contain this "opt-out" mechanism.

When Girocco runs git, it arranges for git to always use a custom
"global" git config file to ensure Girocco always runs with a
consistent Git environment (and Girocco also always disables use
of any system wide git configuration as well for the same reason).

Add the necessary configuration item to "opt-out" of the
"core.sharedrepository" breakage when running an affected Git
version.

This is harmless for older versions of Git (they simply ignore the
setting since they do not know about it) which do not require the
"opt-out" in the first place.

For versions released on or after 2022-04-13, this resolves the
issue for Girocco.

Unfortunately, those versions initially released on 2022-04-12
remain completely incompatible with Girocco.

In addition, because the 2022-04-12 release was for a CVE
(CVE-2022-24765), many distributions of Git that appear to be older,
unaffected versions, backported the CVE fix changes, thus making
them also completely incompatible with Girocco despite them appearing
to be an older, unaffected, version of Git.

Fortunately, it appears that those distributions which initially
backported the CVE fix into older versions of Git have also now
backported the subsequent fix released on 2022-04-13 to fix the fix
for the CVE.

For this reason, there's no attempt added to detect the problematic
versions of Git at this time.  For reasons stated above, simply
checking the Git version number provides inadequate checking in the
face of the backporting that took place for the CVE fix.

Checking for the issue without testing the Git version number remains
problematic as it requires the ability to change the owner of a
file in order to truly check for the incompatibility and that
generally requires super-user privileges which Girocco only currently
requires when installing a chroot jail for ssh fetch/push access.

The affected Git versions that are completely incompatible with
Girocco are expected to not be in use since they were immediately
superseded one day after their release (and the distributions that
performed a backport of the CVE fix have backported the fix for the
CVE fix).