docker: Install qemu-user-static 6.0 to fix segfault

There are issues with qemu-user-static 5.2 crashing when attempting
to allocate guest memory when compiled as a proper statically-linked
binary.

From testing, qemu 6.0 fixes the bug but it's not yet clear which
patch fixes the bug. So until the correct patch is backported to
bullseye, let's install qemu from experimental to pickup the bugfix.

See: #245
See: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=988174

Signed-off-by: Christopher Obbard <chris.obbard@collabora.com>

docker/Dockerfile

@@ -55,7 +55,8 @@ LABEL org.label-schema.docker.cmd 'docker run \
 
 # debos runtime dependencies
 # ca-certificates is required to validate HTTPS certificates when getting debootstrap release file
-RUN apt-get update && \
+RUN echo "deb http://deb.debian.org/debian experimental main" > /etc/apt/sources.list.d/experimental.list && \
+    apt-get update && \
     apt-get install -y --no-install-recommends \
         apt-transport-https \
         binfmt-support \
@@ -78,8 +79,6 @@ RUN apt-get update && \
         linux-image-amd64 \
         parted \
         pkg-config \
-        qemu-system-x86 \
-        qemu-user-static \
         systemd \
         systemd-container \
         u-boot-tools \
@@ -87,6 +86,9 @@ RUN apt-get update && \
         user-mode-linux \
         xz-utils \
         zip && \
+    apt-get install -y --no-install-recommends -t experimental \
+        qemu-system-x86 \
+        qemu-user-static && \
     rm -rf /var/lib/apt/lists/*
 
 COPY --from=builder $GOPATH/bin/debos /usr/local/bin/debos