Stop unit tests from modifying config files

[blonienc]

Description: There's currently a bug where running unit tests (poetry run poe test) will result in .secureli.yaml being modified to include a "scan_patterns" property which is used for unit testing the custom regex scanner feature.

The unit tests need to be updated so that .secureli.yaml isn't updated at all during unit testing. We should instead be mocking the .secureli.yaml file in the tests.

AC: running unit tests locally does not result in any config files being modified