OsStr eq_ignore_ascii_case takes arg by value

Per a comment on #70516 this changes `eq_ignore_ascii_case` to take the generic parameter `S: AsRef<OsStr>` by value instead of by reference.

This is technically a breaking change to an unstable method. I think the only way it would break is if you called this method with an explicit type parameter, ie `my_os_str.eq_ignore_ascii_case::<str>("foo")` becomes `my_os_str.eq_ignore_ascii_case::<&str>("foo")`.

Besides that, I believe it is overall more flexible since it can now take an owned `OsString` for example.

If this change should be made in some other PR (like #80193) then please just close this.

library/std/src/ffi/os_str.rs

@@ -826,7 +826,7 @@ pub fn is_ascii(&self) -> bool {
     /// assert!(!OsString::from("Ferrös").eq_ignore_ascii_case("FERRÖS"));
     /// ```
     #[unstable(feature = "osstring_ascii", issue = "70516")]
-    pub fn eq_ignore_ascii_case<S: ?Sized + AsRef<OsStr>>(&self, other: &S) -> bool {
+    pub fn eq_ignore_ascii_case<S: AsRef<OsStr>>(&self, other: S) -> bool {
         self.inner.eq_ignore_ascii_case(&other.as_ref().inner)
     }
 }