Fix browser extension after-install page
Created by: erzhtor
Closes https://github.com/sourcegraph/sourcegraph/issues/30101.
Description
This PR:
- Fixes the browser extension after-install page, which was broken in https://github.com/sourcegraph/sourcegraph/pull/28837
How to test
sg run bext
- Reinstall the browser extension locally and check that the after-install page is rendered properly.