[flake8-async] allow async generators (ASYNC100) (#13639)

<!--
Thank you for contributing to Ruff! To help us out with reviewing,
please consider the following:

- Does this pull request include a summary of the change? (See below.)
- Does this pull request include a descriptive title?
- Does this pull request include references to any relevant issues?
-->

## Summary

Treat async generators as "await" in ASYNC100.

Fixes #13637

## Test Plan

Updated snapshot

crates/ruff_python_ast/src/helpers.rs

@@ -1004,6 +1004,14 @@ impl Visitor<'_> for AwaitVisitor {
             crate::visitor::walk_expr(self, expr);
         }
     }
+
+    fn visit_comprehension(&mut self, comprehension: &'_ crate::Comprehension) {
+        if comprehension.is_async {
+            self.seen_await = true;
+        } else {
+            crate::visitor::walk_comprehension(self, comprehension);
+        }
+    }
 }
 
 /// Return `true` if a `Stmt` is a docstring.