Add tracking issue for const_arguments_as_str

Author: Sky

Diff for: library/core/src/fmt/mod.rs

@@ -510,7 +510,7 @@ impl<'a> Arguments<'a> {
     /// assert_eq!(format_args!("{}", 1).as_str(), None);
     /// ```
     #[stable(feature = "fmt_as_str", since = "1.52.0")]
-    #[rustc_const_unstable(feature = "const_arguments_as_str", issue = "none")]
+    #[rustc_const_unstable(feature = "const_arguments_as_str", issue = "103900")]
     #[must_use]
     #[inline]
     pub const fn as_str(&self) -> Option<&'static str> {