Debug print char 0 as '\0' rather than '\u{0}'

src/test/ui/half-open-range-patterns/half-open-range-pats-exhaustive-fail.stderr

@@ -50,17 +50,17 @@ LL ~         match $s { $($t)+ => {}
 LL ~         '\u{10fffe}'..='\u{10ffff}' => todo!() }
    |
 
-error[E0004]: non-exhaustive patterns: `'\u{0}'` not covered
+error[E0004]: non-exhaustive patterns: `'\0'` not covered
   --> $DIR/half-open-range-pats-exhaustive-fail.rs:28:8
    |
 LL |     m!('a', ALMOST_MIN..);
-   |        ^^^ pattern `'\u{0}'` not covered
+   |        ^^^ pattern `'\0'` not covered
    |
    = note: the matched value is of type `char`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL ~         match $s { $($t)+ => {}
-LL ~         '\u{0}' => todo!() }
+LL ~         '\0' => todo!() }
    |
 
 error[E0004]: non-exhaustive patterns: `'\u{10ffff}'` not covered