Refactors our use of `slogtest` to instantiate a "standard logger" across most of our tests. This standard logger incorporates https://github.com/coder/slog/pull/217 to also ignore database query canceled errors by default, which are a source of low-severity flakes.
Any test that has set non-default `slogtest.Options` is left alone. In particular, `coderdtest` defaults to ignoring all errors. We might consider revisiting that decision now that we have better tools to target the really common flaky Error logs on shutdown.
fixes#14961
Adding the license and updating entitlements is flaky, especially at the start of our `coderdent` testing because, while the actual modifications to the `entitlements.Set` were threadsafe, we could have multiple goroutines reading from the database and writing to the set, so we could end up writing stale data.
This enforces serialization on updates, so that if you modify the database and kick off an update, you know the state of the `Set` is at least as fresh as your database update.
