Unskip the skipped test / no longer rely on `static` state

[tsimbalar]

In order to be able to get v3.0.1 out as quickly as possible, I marked as skipped a test that worked when run alone, but failed when running the whole test suite.

This was a temporary workaround, but we should get that fixed.

The test is :
LoggerConfigurationExtensionsTests.ReadFromConfigurationSectionThrowsWhenTryingToCallConfigurationMethodWithIConfigurationParam

It is failing because it relies on a static ConfigurationReader._configuration field.

A proper fix would be to no longer rely on static state for that

See discussion : #144 (comment)

I think the long term fix would be to get rid of that static state, but it may be better to release a v3.0.1 bugfix first ?