TEST-46-HOMED: conditionally skip usrquota tests

TEST-46-HOMED: conditionally skip usrquota tests

The tests were failing, because the quota was not enforced.
It seems that we simply don't have privileges to set or display the quota.
The test is running priviled, so this is probably some SELinux:
TEST-46-HOMED.sh[117]: + /usr/lib/systemd/tests/unit-tests/manual/test-display-quota tmpfsquota /dev/shm /tmp
TEST-46-HOMED.sh[1103]: Lacking privileges to query UID quota on /dev/shm: Operation not permitted
TEST-46-HOMED.sh[1103]: Lacking privileges to query UID quota on /tmp: Operation not permitted

If we cannot display the quota, ignore the test results.
In a local run under mkosi, quota is shown and the tests pass. So this is something
about how the testing-farm:fedora-rawhide-x86_64 is configured.