Rollup merge of rust-lang#137061 - progressive-galib:gen_future-closing#76249, r=ibraheemdev

Unstable `gen_future` Feature Tracking

This PR removes the reference to the closed tracking issue **rust-lang#50547** for the `gen_future` feature. Since `gen_future` is an internal feature used in async block desugaring, it does not require a public tracking issue.

#### Changes:
- Replaced `issue = "50547"` with `issue = "none"` in **library/core/src/future/mod.rs**.
- Ensures that it is correctly identified as an internal feature.

#### Rationale:
With this change, the Unstable Book will now state:
> *"This feature has no tracking issue and is therefore likely internal to the compiler, not being intended for general use."*

Closes **rust-lang#76249**. 🚀🦀

Author: jhpratt

library/core/src/future/mod.rs

@@ -46,19 +46,19 @@ pub use self::join::join;
 /// It also simplifies the HIR lowering of `.await`.
 #[lang = "ResumeTy"]
 #[doc(hidden)]
-#[unstable(feature = "gen_future", issue = "50547")]
+#[unstable(feature = "gen_future", issue = "none")]
 #[derive(Debug, Copy, Clone)]
 pub struct ResumeTy(NonNull<Context<'static>>);
 
-#[unstable(feature = "gen_future", issue = "50547")]
+#[unstable(feature = "gen_future", issue = "none")]
 unsafe impl Send for ResumeTy {}
 
-#[unstable(feature = "gen_future", issue = "50547")]
+#[unstable(feature = "gen_future", issue = "none")]
 unsafe impl Sync for ResumeTy {}
 
 #[lang = "get_context"]
 #[doc(hidden)]
-#[unstable(feature = "gen_future", issue = "50547")]
+#[unstable(feature = "gen_future", issue = "none")]
 #[must_use]
 #[inline]
 pub unsafe fn get_context<'a, 'b>(cx: ResumeTy) -> &'a mut Context<'b> {