gitlab-ci: Disable the s390x storage key test (which fails now with TCG)

Commit 429c9cc2 ("s390x: skey: Test for ADDRESSING exceptions") added
some new tests which require the latest and greatest QEMU, which is
not available in the distros yet, so the skey test is currently failing
in the CI. Disable it for the time being, we'll switch it on again once
the distros feature a QEMU with the bug fix.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Message-Id: <20211021182113.818393-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>