Allow Property.check to work with Property<_> and not just Property<unit>

Fluent assertion libraries like FluentAssertions generally make the test implementation return a non-`unit` value. `Property.check` and similar require `Property`, which means I have to explicitly `|> ignore` the result of the fluent assertion chain. This explicit ignoring is not necessary if not using properties (for example, xUnit by itself allows test functions to return arbitrary values), and I can't see a good reason why `Property.check` and similar could not just ignore the generic value and therefore work with any `Property<_>`.