fix(docker): add xauth to Windows build image to fix xvfb-run

xvfb-run requires xauth to create the virtual display cookie;
without it the Wine/Python installer step fails with exit code 3

contrib/windows/Dockerfile

@@ -8,7 +8,7 @@ RUN dpkg --add-architecture i386 && \
     apt-get update && apt-get install -y --no-install-recommends \
     wine wine64 \
     python3 python3-pip python3-venv libpython3.11 \
-    binutils wget xvfb ca-certificates \
+    binutils wget xvfb xauth ca-certificates \
     && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /build