Add test for issue-71611

Author: JohnTitor

src/test/ui/const-generics/issues/issue-71611.rs

@@ -0,0 +1,9 @@
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+fn func<A, const F: fn(inner: A)>(outer: A) {
+    //~^ ERROR: using function pointers as const generic parameters is forbidden
+    F(outer);
+}
+
+fn main() {}

src/test/ui/const-generics/issues/issue-71611.stderr

@@ -0,0 +1,8 @@
+error: using function pointers as const generic parameters is forbidden
+  --> $DIR/issue-71611.rs:4:21
+   |
+LL | fn func<A, const F: fn(inner: A)>(outer: A) {
+   |                     ^^^^^^^^^^^^
+
+error: aborting due to previous error
+