Update bastion-of-the-turbofish.rs

The original tweet in the chain linked to, and thus the through line of links back to Anna's tweet where she named the turbofish (https://web.archive.org/web/20210911061514/https://twitter.com/whoisaldeka/status/914914008225816576) are lost as the user whoisaldeka has deleted their twitter account.

Switching to an archive link preserves this through line, allowing someone to browse back to see the point at which Anna created the turbofish, as was the original intent of including this context.

Author: LLBlumire

tests/ui/parser/bastion-of-the-turbofish.rs

@@ -34,7 +34,7 @@
 
 // See https://github.com/rust-lang/rust/pull/53562
 // and https://github.com/rust-lang/rfcs/pull/2527
-// and https://twitter.com/garblefart/status/1393236602856611843
+// and https://web.archive.org/web/20211010063452/https://twitter.com/garblefart/status/1393236602856611843
 // for context.
 
 fn main() {