Add test case for methods in traits that take uninhabited types

These should not currently be linted.

Author: varkor

src/test/ui/uninhabited/uninhabited-function-parameter-warning.rs

@@ -8,10 +8,14 @@ fn foo(a: (), b: Void) { //~ ERROR functions with parameters of uninhabited type
 
 trait Foo {
     fn foo(a: Self);
+
+    fn bar(b: Void);
 }
 
 impl Foo for Void {
     fn foo(a: Void) {} // ok
+
+    fn bar(b: Void) {} // ok
 }
 
 fn main() {}