Astro v6 AstroContainer still requires experimental_ prefix

In Astro v6.1.6, astro/container only exports experimental_AstroContainer, not AstroContainer. The non-prefixed name does not exist despite v6 being a major release. Import as: import { experimental_AstroContainer as AstroContainer } from "astro/container". This tripped up the migration because the upgrade guide implied the experimental prefix would be dropped.