dockerfiles: bump tricore cross compiler container to Debian 11

With the release of version 12 on June 10, 2023, Debian 10 is
not supported anymore.  Modify the cross compiler container to
build on a newer version.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tests/docker/dockerfiles/debian-tricore-cross.docker

@@ -9,7 +9,7 @@
 #
 # SPDX-License-Identifier: GPL-2.0-or-later
 #
-FROM docker.io/library/debian:buster-slim
+FROM docker.io/library/debian:11-slim
 
 MAINTAINER Philippe Mathieu-Daudé <f4bug@amsat.org>