Jorwoods/quota tiers allow null

[jorwoods]

Allow setting site.user_quota equal to None if license levels are set.

[jorwoods]

Black is incompatible with Click 8.1.0. Will rerun tests after black gets fixed.

Issue: psf/black#2964 (comment)

[jacalata]

Here's a test that passes without your change: can you add it and update?
def test_null_site_quota(self) -> None:
test_site = TSC.SiteItem('testname', 'testcontenturl', tier_explorer_capacity=1, user_quota=None)
assert test_site.tier_explorer_capacity == 1
with self.assertRaises(ValueError):
test_site.user_quota = 1
test_site.tier_explorer_capacity = None
test_site.user_quota = 1

[jorwoods]

I also modified the existing test_update for sites to fail appropriately if the fix is not in place. Added a new test for the new override method. Added the test proposed by @jacalata to exhibit failures when setting user_quota directly to some non-null value, but work when None.

[jacalata]

thanks!