Lighthouse: Fix port and run synchronously
Created by: umpox
Trying synchronous runs again. I think the last time we got failures after merging because I merged the HTTPS dev server changes which mean the HTTP server was now on port 3080
instead
Note: I ran hourly builds overnight a cron job, didn't get a failure: https://buildkite.com/sourcegraph/sourcegraph-async/builds?branch=tr%2Flighthouse-finally
Repeat of https://github.com/sourcegraph/sourcegraph/pull/25947