Update the .stderr to include the backticks

Author: Lythenas

tests/ui/unit_cmp.stderr

@@ -22,31 +22,31 @@ LL | |         false;
 LL | |     } {}
    | |_____^
 
-error: assert_eq of unit values detected. This will always succeed
+error: `assert_eq` of unit values detected. This will always succeed
   --> $DIR/unit_cmp.rs:24:5
    |
 LL |     assert_eq!((), ());
    |     ^^^^^^^^^^^^^^^^^^^
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
-error: debug_assert_eq of unit values detected. This will always succeed
+error: `debug_assert_eq` of unit values detected. This will always succeed
   --> $DIR/unit_cmp.rs:25:5
    |
 LL |     debug_assert_eq!((), ());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
-error: assert_ne of unit values detected. This will always fail
+error: `assert_ne` of unit values detected. This will always fail
   --> $DIR/unit_cmp.rs:27:5
    |
 LL |     assert_ne!((), ());
    |     ^^^^^^^^^^^^^^^^^^^
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
-error: debug_assert_ne of unit values detected. This will always fail
+error: `debug_assert_ne` of unit values detected. This will always fail
   --> $DIR/unit_cmp.rs:28:5
    |
 LL |     debug_assert_ne!((), ());