Resolve dead_code warning in test

    warning: enum `DeprecatedFrom` is never used
      --> tests/test_lints.rs:79:14
       |
    79 |     pub enum DeprecatedFrom {
       |              ^^^^^^^^^^^^^^
       |
       = note: `#[warn(dead_code)]` on by default

Author: dtolnay

tests/test_lints.rs

@@ -93,4 +93,6 @@ fn test_deprecated() {
     let _ = DeprecatedEnum::Variant;
     #[allow(deprecated)]
     let _ = DeprecatedVariant::Variant;
+    #[allow(deprecated)]
+    let _ = DeprecatedFrom::Variant(DeprecatedStruct);
 }