build: upgrade docker image to use debian:stable-20240722-slim

crates/cli/src/alerts/tests/history.rs

@@ -35,6 +35,8 @@ fn when_history_has_expired_then_message_is_passed() {
     let result = history.sendable(user_notification);
     let_assert!(Some(user_notification) = result);
 
+    std::thread::sleep(dur);
+    // twice the expiry duration to avoid things happening in the wrong order
     std::thread::sleep(dur);
 
     // after dur, message has expired, so is still valid