Update rustc_on_unimplemented message for Step

Author: estebank

library/core/src/iter/range.rs

@@ -22,6 +22,7 @@ unsafe_impl_trusted_step![AsciiChar char i8 i16 i32 i64 i128 isize u8 u16 u32 u6
 /// The *predecessor* operation moves towards values that compare lesser.
 #[rustc_diagnostic_item = "range_step"]
 #[rustc_on_unimplemented(
+    message = "`std::ops::Range<{Self}>` is not an iterator",
     note = "`Range` only implements `Iterator` for select types in the standard library, \
             particularly integers; to see the full list of types, see the documentation for the \
             unstable `Step` trait"

tests/ui/range/range-1.rs

@@ -7,7 +7,7 @@ pub fn main() {
 
     // Bool => does not implement iterator.
     for i in false..true {}
-    //~^ ERROR `bool: Step` is not satisfied
+    //~^ ERROR `std::ops::Range<bool>` is not an iterator
 
     // Unsized type.
     let arr: &[_] = &[1, 2, 3];

tests/ui/range/range-1.stderr

@@ -4,7 +4,7 @@ error[E0308]: mismatched types
 LL |     let _ = 0u32..10i32;
    |                   ^^^^^ expected `u32`, found `i32`
 
-error[E0277]: the trait bound `bool: Step` is not satisfied
+error[E0277]: `std::ops::Range<bool>` is not an iterator
   --> $DIR/range-1.rs:9:14
    |
 LL |     for i in false..true {}

tests/ui/trait-bounds/unstable-trait-suggestion.stderr

@@ -16,7 +16,7 @@ help: consider restricting type parameter `T` with unstable trait `Unstable`
 LL | pub fn bar<T: Unstable>(t: T) {
    |             ++++++++++
 
-error[E0277]: the trait bound `T: Step` is not satisfied
+error[E0277]: `std::ops::Range<T>` is not an iterator
   --> $DIR/unstable-trait-suggestion.rs:17:14
    |
 LL |     for _ in t {}