Muted alert started to send notifications to Slack

### Environment SaaS (https://sentry.io/) ### Steps to Reproduce 1. Create an Issue Alert that sends Slack notifications on every new issue 2. Mute the alert 3. Wait a month (I hate how non-reproducible it is, I'm so sorry, but this is what happens to us) Note: These issues are not new at all. The Sentry project has been creating and updating issues constantly all this time- it's just now that the alert started to trigger, and send notifications to Slack <img width="1063" height="676" alt="Image" src="https://github.com/user-attachments/assets/ca369f03-f1ba-4bf4-a9c9-128e2bcb5f3b" /> <img width="1047" height="277" alt="Image" src="https://github.com/user-attachments/assets/d786f2c7-d845-4126-b9b3-c95fce66b2ad" /> ### Expected Result The alert doesn't send any notifications for as long as it stays muted ### Actual Result We started to get Slack notifications out of the blue. Luckily it's an internal testing channel and it's not bothering the developers yet :) Unmuting it and muting it again seems to have stopped them from coming, but I thought it's worth to report what happened either way. <img width="952" height="370" alt="Image" src="https://github.com/user-attachments/assets/34f81b2f-41dc-484b-983b-a3d409c5d07d" /> ### Product Area Alerts ### Link _No response_ ### DSN _No response_ ### Version _No response_