Feature flags: Do not know how to serialize a BigInt type error

Bug description

Please describe.
The above is showing up on a feature flag page If you are on PostHog Cloud it would be really valuable if you can share any links where the problem occurs. This speeds up our ability to troubleshoot tremendously.

How to reproduce

Environment

• PostHog Cloud US, project ID: [please provide from https://app.posthog.com/settings/project-details#variables]
• PostHog Cloud EU, project ID: [please provide from 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"), version/commit: [please provide]

Additional context

Thank you for your bug report – we love squashing them!