ci: convert last remnant from "meson setup" migration

We missed one.

Fixes: 254c5fc752 ("Switch to "meson setup"")

.builds/alpine.yml

@@ -32,7 +32,7 @@ tasks:
       sudo ninja -C build install
   - build-features-disabled: |
       cd wlroots
-      meson build --reconfigure -Dauto_features=disabled
+      meson setup build --reconfigure -Dauto_features=disabled
       ninja -C build
   - tinywl: |
       cd wlroots/tinywl