Add libdbus-glib-1-dev to CI build

For parole and xfce4-screensaver, to be removed when these issues are
solved:
apps/parole#114
apps/xfce4-screensaver#153

Dockerfile

@@ -11,6 +11,7 @@ RUN apt-get update \
   libwayland-bin libwayland-dev libgtk-layer-shell-dev \
   libcurl4-openssl-dev libffmpegthumbnailer-dev libgsf-1-dev libpoppler-glib-dev libopenrawgnome-dev libgepub-0.7-dev \
   polkitd clang-format \
+  libdbus-glib-1-dev \
   && rm -rf /var/lib/apt/lists/*
 
 # Build and install the latest tag for all Xfce core libraries