Update ui tests with 2021-edition diagnostics

Author: dtolnay

tests/ui/bare-trait-object.stderr

@@ -1,17 +1,10 @@
-error: trait objects without an explicit `dyn` are deprecated
+error[E0782]: trait objects must include the `dyn` keyword
   --> tests/ui/bare-trait-object.rs:11:16
    |
 11 | impl Trait for Send + Sync {
    |                ^^^^^^^^^^^
    |
-   = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
-   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-note: the lint level is defined here
-  --> tests/ui/bare-trait-object.rs:1:9
-   |
-1  | #![deny(bare_trait_objects)]
-   |         ^^^^^^^^^^^^^^^^^^
-help: use `dyn`
+help: add `dyn` keyword before this trait
    |
 11 | impl Trait for dyn Send + Sync {
    |                +++