⚡️Site slow when offline

## Bug Report

Browsers accept about 5 concurrent requests, problem is when we are offline, Posthog retry immediately the requests after failing, blocking / pausing the other requests.

Reduce Posthog `retry_count` to 1:
https://product.docs.numerique.gouv.fr/e/?retry_count=5&ip=0&_=1766011151932&ver=1.298.0