Dashboard - Don't handle having 3 the same visualisation columns in the widget after saving

### Environment SaaS (https://sentry.io/) ### Steps to Reproduce 1. Create widget 2. Create 3 the same columns in the vizualisation section 3. Hit save <img width="1012" height="243" alt="Image" src="https://github.com/user-attachments/assets/7f5e2c86-7958-4df2-af55-6dd172978f3c" /> See Sentry issue: https://sentry.sentry.io/issues/7050468989/events/67207eae10054f9ca068593a4bcbcd6f/ ### Expected Result Saved widget shows correctly ### Actual Result Internal error. Please try again. https://demo.sentry.io/dashboard/127293/?project=5808623&statsPeriod=7d <img width="2446" height="446" alt="Image" src="https://github.com/user-attachments/assets/429e59d8-cd05-48ca-aaf4-0a7ff6f9491d" /> ### Product Area Dashboards ### Link _No response_ ### DSN _No response_ ### Version _No response_