## Summary
- Temporarily revert composite action to `docker build` so we can build the runner image (chicken-and-egg: current runner v2.5.0 doesn't have buildx)
- Bump runner label to `v2.5.1` so after sync the new runner image (with buildx) gets used
## Deployment plan
1. Merge this PR
2. Tag `forgejo-runner-v2.5.1` — builds with legacy `docker build` (one last time)
3. Sync forgejo-runner in ArgoCD to pick up the v2.5.1 label
4. Follow-up PR: switch action back to `docker buildx build`
5. Tag `nettest-v0.12.0` to verify buildx works end-to-end
Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/148
Erich Blume
f0ac04fb8a