[ruff] fix async comprehension false positive (RUF029) (#11070)

## Summary

- Fix #11043 

## Test Plan

Added the false positive code in the test fixture.

crates/ruff_linter/resources/test/fixtures/ruff/RUF029.py

@@ -69,3 +69,7 @@ async def foo(self):
 def foo():
     async def fail_4c():  # RUF029: the /inner/ function does not await
         pass
+
+
+async def test():
+    return [check async for check in async_func()]

crates/ruff_linter/src/rules/ruff/rules/unused_async.rs

@@ -84,6 +84,11 @@ impl<'a> preorder::PreorderVisitor<'a> for AsyncExprVisitor {
             _ => preorder::walk_stmt(self, stmt),
         }
     }
+    fn visit_comprehension(&mut self, comprehension: &'a ast::Comprehension) {
+        if comprehension.is_async {
+            self.found_await_or_async = true;
+        }
+    }
 }
 
 /// Very nearly `crate::node::StmtFunctionDef.visit_preorder`, except it is specialized and,