Disable clippy lint 'self-named-constructors' for Null::null()

The following warning (as error) was generated:

-------------------------------------------------------
error: constructor `null` has the same name as the type
    --> gdnative-core\src\object.rs:1023:5
     |
1023 | /     pub fn null() -> Self {
1024 | |         Null(PhantomData)
1025 | |     }
     | |_____^
     |
     = note: `-D clippy::self-named-constructors` implied by `-D clippy::style`
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#self_named_constructors
-------------------------------------------------------

Author: Bromeon

gdnative-core/src/object.rs

@@ -1017,8 +1017,10 @@ pub trait AsVariant: AsArg<<Self as AsVariant>::Target> {
 pub struct Null<T>(PhantomData<T>);
 
 impl<T: GodotObject> Null<T> {
-    /// Creates an explicitly null reference that can be used as a method argument.
+    /// Creates an explicit null reference that can be used as a method argument.
+    // TODO consider something more idiomatic, like module::null::<T>(), similar to std::ptr::null()
     #[inline]
+    #[allow(clippy::self_named_constructors)]
     pub fn null() -> Self {
         Null(PhantomData)
     }