Change description from compiletest to regression test

Co-authored-by: 许杰友 Jieyou Xu (Joe) <39484203+jieyouxu@users.noreply.github.com>

Author: LFS6502

tests/ui/idk-what-to-call-this.rs

@@ -1,5 +1,5 @@
 //@ check-pass
-//compiletest for #107883: Returning `impl Fn(T) -> impl Trait`
+// Regression test for #107883: Returning `impl Fn(T) -> impl Trait`
 #![feature(impl_trait_in_fn_trait_return)]
 #![feature(unboxed_closures)] // only for `h`