Doc: Extend for tuples to be stabilized in 1.85.0

I assumed the RUSTC_CURRENT_VERSION would be replaced automatically, but
it doesn't look like it on the nightly docs page. Sorry!

library/core/src/iter/traits/collect.rs

@@ -494,7 +494,7 @@ impl Extend<()> for () {
 
 macro_rules! spec_tuple_impl {
     ( ($ty_name:ident, $var_name:ident, $extend_ty_name: ident, $trait_name:ident, $default_fn_name:ident, $cnt:tt), ) => {
-        spec_tuple_impl!($trait_name, $default_fn_name, #[doc(fake_variadic)] #[doc = "This trait is implemented for tuples up to twelve items long. The `impl`s for 1- and 3- through 12-ary tuples were stabilized after 2-tuples, in RUSTC_CURRENT_VERSION."] => ($ty_name, $var_name, $extend_ty_name, $cnt),);
+        spec_tuple_impl!($trait_name, $default_fn_name, #[doc(fake_variadic)] #[doc = "This trait is implemented for tuples up to twelve items long. The `impl`s for 1- and 3- through 12-ary tuples were stabilized after 2-tuples, in 1.85.0."] => ($ty_name, $var_name, $extend_ty_name, $cnt),);
     };
     ( ($ty_name:ident, $var_name:ident, $extend_ty_name: ident, $trait_name:ident, $default_fn_name:ident, $cnt:tt), $(($ty_names:ident, $var_names:ident,  $extend_ty_names:ident, $trait_names:ident, $default_fn_names:ident, $cnts:tt),)*) => {