Adding Series Breakdown to SQL generated charts doesn't save

[jt-MV]

Bug Description

Created Insights via SQL

1. Adding a Series Breakdown to X-axis should look at this (dummy data, breaking down month by week number)
   
2. Pressing Save will show the Insight with correct format
   
3. However, new Series Breakdown is not persisted. Refreshing or add it to dashboard will revert back to Series Breakdown removed
   

Debug info

- [ ] PostHog Cloud, Debug information: [please copy/paste from https://us.posthog.com/settings/project-details#variables or https://eu.posthog.com/settings/project-details#variables]
- [ ] PostHog Hobby self-hosted with `docker compose`, version/commit: [please provide]
- [ ] PostHog self-hosted with Kubernetes (deprecated, see [`Sunsetting Kubernetes support`](https://posthog.com/blog/sunsetting-helm-support-posthog)), version/commit: [please provide]