We're not actually, but that doesn't mean we shouldn't change this.

This test was originally intended to just validate that saved auths actually get saved and that we get back out what we expect from `MongoClient#auths`. With the introduction of validate_credentials though which also normalizes values like `source` and `mechanism` the auth set can actually get modified if you left those values nil. The addition of `validate_credentials` to this test is just to account for this change.

Even though testing validate here wasn't the intent, it makes sense to change this to reflect what's actually happening. I may change this to `should "save and validate the authentication"`.