Update compiler/rustc_middle/src/ty/sty.rs

Co-authored-by: Oli Scherer <github35764891676564198441@oli-obk.de>

Author: lcnr

compiler/rustc_middle/src/ty/sty.rs

@@ -209,7 +209,7 @@ pub enum TyKind<'tcx> {
     /// * the `impl Trait` ast::Ty node,
     /// * or the `type Foo = impl Trait` declaration
     ///
-    /// For RTIT the substitutions are for the generics of the function,
+    /// For RPIT the substitutions are for the generics of the function,
     /// while for TAIT it is used for the generic parameters of the alias.
     Opaque(DefId, SubstsRef<'tcx>),