fix(ci): build-arch fails — actions/checkout needs Node, archlinux image has none

actions/checkout@v4 is a JS action requiring a Node runtime to execute;
archlinux:base-devel doesn't ship one, so the job failed immediately
with "node: executable file not found". The job only needs one file
(packaging/pacman/PKGBUILD), so fetch it via curl from Gitea's raw
endpoint instead of checking out the whole repo. Also drop pacman -Syu
to -Sy (sync-only) — a full system upgrade isn't needed in a
throwaway container and risks partial-upgrade/keyring failures.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -290,10 +290,18 @@ jobs:
     container:
       image: archlinux:base-devel
     steps:
-      - uses: actions/checkout@v4
-
+      # actions/checkout@v4 is a Node.js action and archlinux:base-devel has
+      # no Node runtime — it fails with "node: executable file not found".
+      # This job only needs one file, so skip checkout and fetch it directly
+      # from Gitea's raw endpoint instead.
       - name: Install build tools
-        run: pacman -Syu --noconfirm --needed curl python
+        run: pacman -Sy --noconfirm --needed curl python
+
+      - name: Fetch PKGBUILD
+        run: |
+          mkdir -p packaging/pacman
+          curl -sf "$GITEA_URL/LotusGuild/cinny-desktop/raw/branch/main/packaging/pacman/PKGBUILD" \
+            -o packaging/pacman/PKGBUILD
 
       - name: Set package version
         env: