fix: restore continue-on-error on checkout (runner can't fetch Gitea)

The act_runner on .228 cannot git-fetch from git.tx1138.com via the
actions/checkout action (auth/network issue). Without continue-on-error
the build dies before the ~/archy rsync fallback can run. Restore it
so the fallback works. The red cross on checkout is cosmetic — the
fallback step provides the correct code.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-iso-dev.yml

@@ -16,6 +16,7 @@ jobs:
         with:
           fetch-depth: 1
         timeout-minutes: 5
+        continue-on-error: true
 
       - name: Sync from local repo (fallback if checkout failed)
         run: |