Add regression test for rust-lang#71547

Signed-off-by: Yuki Okushi <jtitor@2k36.org>

Author: JohnTitor

src/test/ui/const-generics/issues/issue-71547.rs

@@ -0,0 +1,18 @@
+// check-pass
+
+#![feature(adt_const_params)]
+#![allow(incomplete_features)]
+
+pub trait GetType<const N: &'static str> {
+    type Ty;
+    fn get(&self) -> &Self::Ty;
+}
+
+pub fn get_val<T>(value: &T) -> &T::Ty
+where
+    T: GetType<"hello">,
+{
+    value.get()
+}
+
+fn main() {}