fix(ci): pacman -Syu before build to refresh stale package DB

Runner container has a cached pacman DB that lists package versions
already rotated off the mirrors, causing 404s when makepkg -s tries
to pull makedepends (gtk4, mesa, llvm-libs). Sync the DB first.

.gitea/workflows/build-and-publish.yaml

@@ -29,6 +29,9 @@ jobs:
 
           echo "Changed packages: $CHANGED"
 
+          # Sync pacman DB so -s can pull current versions (Arch rolling)
+          sudo pacman -Syu --noconfirm
+
           for pkg in $CHANGED; do
             echo "==> Building $pkg"
             cd "$pkg"