Fix test isolation problem with settings assignment

[AlanCoding]

SUMMARY

These tests introduced a flaky failure:

  File "/awx_devel/awx/main/tests/unit/test_settings.py", line 32, in test_default_settings
    assert default_val == snapshot_val, f'Setting for {k} does not match shapshot:\nsnapshot: {snapshot_val}\ndefault: {default_val}'
AssertionError: Setting for OPTIONAL_API_URLPATTERN_PREFIX does not match shapshot:
  snapshot: 
  default: foo
assert 'foo' == ''

AFAIK this was only observed in DAB with downstream testing, but I see no reason it wouldn't also occur in AWX since it's a very generic reason that it happens. The stale "foo" value is left around at the end of the test.

ISSUE TYPE

• Bug, Docs Fix or other nominal change

COMPONENT NAME

• API

[chrismeyersfsu]

Hmm, thought I fixed this here #15237

[AlanCoding]

Maybe so.