Fix false positive for unused_unit (#14962)

Given a type alias as follows, clippy would detect a false positive for
`unused_unit`.

```rust
type UnusedParensButNoUnit = Box<dyn (Fn())>;
```

changelog: [`unused_unit`]: fix false positive for `Fn` bounds

Author: llogiq

clippy_lints/src/unused_unit.rs

@@ -109,6 +109,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedUnit {
             && let AssocItemConstraintKind::Equality { term: Term::Ty(hir_ty) } = constraints[0].kind
             && args.span_ext.hi() != poly.span.hi()
             && !hir_ty.span.from_expansion()
+            && args.span_ext.hi() != hir_ty.span.hi()
             && is_unit_ty(hir_ty)
         {
             lint_unneeded_unit_return(cx, hir_ty.span, poly.span);

tests/ui/unused_unit.edition2021.fixed

@@ -143,4 +143,10 @@ mod issue14577 {
             todo!()
         }
     }
-}
+}
+
+mod pr14962 {
+    #[allow(unused_parens)]
+    type UnusedParensButNoUnit = Box<dyn (Fn())>;
+}
+

tests/ui/unused_unit.edition2024.fixed

@@ -143,4 +143,10 @@ mod issue14577 {
             todo!()
         }
     }
-}
+}
+
+mod pr14962 {
+    #[allow(unused_parens)]
+    type UnusedParensButNoUnit = Box<dyn (Fn())>;
+}
+

tests/ui/unused_unit.rs

@@ -143,4 +143,10 @@ mod issue14577 {
             todo!()
         }
     }
-}
+}
+
+mod pr14962 {
+    #[allow(unused_parens)]
+    type UnusedParensButNoUnit = Box<dyn (Fn())>;
+}
+