Expand where negative supertrait specific error is shown

Fix #58857.

src/test/ui/issues/issue-58857.rs

@@ -0,0 +1,7 @@
+struct Conj<A> {a : A}
+trait Valid {}
+
+impl<A: !Valid> Conj<A>{}
+//~^ ERROR negative trait bounds are not supported
+
+fn main() {}

src/test/ui/issues/issue-58857.stderr

@@ -0,0 +1,8 @@
+error: negative trait bounds are not supported
+  --> $DIR/issue-58857.rs:4:7
+   |
+LL | impl<A: !Valid> Conj<A>{}
+   |       ^^^^^^^^ help: remove the trait bound
+
+error: aborting due to previous error
+