[ruff] Clarify intentional async contexts for unused-async (RUF029)

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

@@ -18,7 +18,11 @@ use crate::rules::fastapi::rules::is_fastapi_route;
 /// ## Why is this bad?
 /// Declaring a function `async` when it's not is usually a mistake, and will artificially limit the
 /// contexts where that function may be called. In some cases, labeling a function `async` is
-/// semantically meaningful (e.g. with the trio library).
+/// semantically meaningful. For example, an async test or callback may need to run in an async
+/// execution context, even if it only uses a `ContextVar`.
+///
+/// If the async context is intentional, add an actual await expression, such as
+/// `await asyncio.sleep(0)`, or disable this rule for the function.
 ///
 /// ## Example
 /// ```python