Allows collectors and subscribers to stash their own `Dispatch`
without causing a memory leak.

This was creating an `&&'static (dyn Collect + ...)` rather than copying
the `&'static (dyn Collect + ...)` into the `WeakDispatch` struct, and
the reference to a static reference to a `dyn Collect + ...` doesn't
forward trait impls. Removing the `&` un-breaks this.