ci(upstream-sync): allow incomplete LFS push

git-lfs's pre-push hook rejects pushes that reference LFS objects the
local checkout doesn't have. Since we skipped smudge on checkout
(GIT_LFS_SKIP_SMUDGE=1), no LFS content is local. But we're only
pushing branch pointers — no new LFS bytes to upload. Tell lfs to
allow the incomplete push via 'git config lfs.allowincompletepush
true', per the hint the hook itself prints.

.gitea/workflows/upstream-sync.yml

@@ -54,6 +54,11 @@ jobs:
           set -euo pipefail
           git config user.name "sulkta-bot"
           git config user.email "bot@sulkta.com"
+          # git-lfs pre-push hook refuses incomplete pushes — which triggers
+          # here because we skipped LFS smudge on checkout, so local LFS
+          # objects are absent. We're only pushing branch pointers (no new
+          # LFS content), so allow incomplete.
+          git config lfs.allowincompletepush true
           OLD=$(git rev-parse --short HEAD)
           echo "main was at $OLD"
           if git merge --ff-only upstream/develop; then