error: use of deprecated struct `OldHeader`: Do not use
  --> tests/ui-nightly/absence_of_deprecated_warning.rs:31:12
   |
31 | impl T for OldHeader {}
   |            ^^^^^^^^^
   |
note: the lint level is defined here
  --> tests/ui-nightly/absence_of_deprecated_warning.rs:14:9
   |
14 | #![deny(deprecated)]
   |         ^^^^^^^^^^