.gitlab-ci.yml: the second comparison is a no-op in docker because the user already exists

.gitlab-ci.yml

@@ -20,7 +20,9 @@ build:
     test -d /srv/chroot/unstable-sbuild || sbuild-createchroot --debootstrap=mmdebstrap --alias=sid unstable /srv/chroot/unstable-sbuild http://deb.debian.org/debian
     test -d /srv/chroot/unstable-arm64-sbuild || sbuild-createchroot --debootstrap=mmdebstrap --alias=sid --arch=arm64 unstable /srv/chroot/unstable-arm64-sbuild http://deb.debian.org/debian
     test -d /srv/chroot/testing-sbuild || sbuild-createchroot --debootstrap=mmdebstrap testing /srv/chroot/testing-sbuild http://deb.debian.org/debian
-    id build >/dev/null || adduser --gecos build --disabled-password build
-    id build >/dev/null || adduser build sbuild
+    if ! id build 2>/dev/null; then
+        adduser --gecos build --disabled-password build
+        adduser build sbuild
+    fi
     chown build -R .
     runuser build -c sh -x ./build.sh 2>&1 | ./filter-output