I think Codeberg.org is not doing the (normally very fast) Gitea any favors here, because it's hosted on Hetzner in Germany. Lighthouse may only throttle the connection further.
Where are the tests being run from?
Is there any way to control for network latency (maybe subtract the ICMP rtt from the tests?)
This has been brought up many times, but latency and bandwidth is controlled for with Lighthouse. The same tests have also been run from Germany without appreciably different results. It's also easy to run the test suite yourself if you have an hour of compute time to spare:
The goal here isn't to compare forge software (that would require a completely different approach to level the playing field), but to compare hosted options. The test suite is easily extended with other hosts or pages, and a few people have tested against their own Gitea instance - usually it ranks somewhere just above the middle of the pack.
Where are the tests being run from?
Is there any way to control for network latency (maybe subtract the ICMP rtt from the tests?)
You might consider comparing it to other Gitea instances like https://try.gitea.io/ (Digital Ocean / USA), https://mirror.git.trinitydesktop.org/ (Czech Republic) or https://gitea.com/ (China), but I guess Codeberg is probably the most representative instance for public use.