Fix missing diagnostic span for impl Trait with const generics

src/test/ui/const-generics/min_const_generics/impl-trait-with-const-arguments.rs

@@ -0,0 +1,22 @@
+#![feature(min_const_generics)]
+
+trait Usizer {
+    fn m(self) -> usize;
+}
+
+fn f<const N: usize>(u: impl Usizer) -> usize {
+    N + u.m()
+}
+
+struct Usizable;
+
+impl Usizer for Usizable {
+    fn m(self) -> usize {
+        16
+    }
+}
+
+fn main() {
+    assert_eq!(f::<4usize>(Usizable), 20usize);
+//~^ ERROR cannot provide explicit generic arguments when `impl Trait` is used in argument position
+}

src/test/ui/const-generics/min_const_generics/impl-trait-with-const-arguments.stderr

@@ -0,0 +1,8 @@
+error[E0632]: cannot provide explicit generic arguments when `impl Trait` is used in argument position
+  --> $DIR/impl-trait-with-const-arguments.rs:20:20
+   |
+LL |     assert_eq!(f::<4usize>(Usizable), 20usize);
+   |                    ^^^^^^ explicit generic argument not allowed
+
+error: aborting due to previous error
+