[Monolog] Only skip real exceptions

[wjzijderveld]

When adding a exception property to the monolog context, it would get skipped regardless if the exception was used as hint or not.

[wjzijderveld]

I can understand that, in a weird way it's a BC break. Personally consider it a bugfix, as PSR-3 states that the context can contain anything and would need to be verified if it's actually an Exception as it can be anything. And currently this data is completely dropped when send to Sentry, which is super confusing.