The runner.arch context isn't populated for job-level if conditions
on Gitea Actions, so the previous guard didn't skip on ARM64 Gitea
runners. Switch to checking github.server_url, which is reliably
'https://github.com' on GitHub-hosted runs and the Gitea host
everywhere else.
The hassfest and HACS validator actions both depend on amd64-only
Docker images (ghcr.io/home-assistant/hassfest, hacs/action). On
ARM64 runners — like the Gitea Actions instance hosting this fork —
those images pull but fail with "exec format error" because no
multi-arch image is published.
Validation still runs on GitHub's amd64 ubuntu-latest runners, where
it actually matters for HACS distribution.
thatguygriff
Sebastien Lavoie