void_checks: allow assigning any future to a FutureOr<void>

[frmrgr]

Describe the quick-fix

import 'dart:async';

void foo(FutureOr<void> x) {}

void main() {
  final intFuture = Future<int>.value(1);
  foo(intFuture); // <-- This lints
  foo((intFuture as dynamic) as FutureOr<int>); // <-- This is allowed
}

It would be great if any future could be passed into a FutureOr<void> argument. Anyway, the only reasonable thing is to await it; and passing a FutureOr<Whatever> is already allowed.

Basically remove the && ... part from the rule.