CI: Enable X11 and Wayland backends for Autotools

Enabling one backend (Broadway, in commit 1882ff9b) implicitly disabled
all the others, which was probably not intentional. Bring the Autotools
build into line with Meson.

Signed-off-by: Simon McVittie <smcv@debian.org>

.gitlab-ci/test-docker-autotools.sh

@@ -11,6 +11,8 @@ cd _build
 ../autogen.sh \
     --enable-cloudproviders \
     --enable-broadway-backend \
+    --enable-wayland-backend \
+    --enable-x11-backend \
     --enable-xinerama \
     --enable-gtk-doc
 make -j8