travis: protect the systemd organization on Fuzzit from forks

travis: protect the systemd organization on Fuzzit from forks

Now that v243 is out, the script has been pulled by forks that are
activated on Travis CI. As a result, all those forks have started to send
their fuzzers to Fuzzit inadvertently consuming our CPUs along the way.
Let's prevent this by bailing out early if the script is run outside of
the systemd repository.

(cherry picked from commit 64d0f7042dfbaa306e16996d2fbb331ee7d59dc8)

Gbp-Pq: Name travis-protect-the-systemd-organization-on-Fuzzit-from-fo.patch