configure: use debian-all-test-cross for mipsel tcg tests

Although we have had the mips compilers in all-test-cross for a while we had been surviving using the mipsel cross compiler image. However when that was removed we missed updating the container to use. Fixes: 366bb88e785 (buildsys: Remove MIPS cross containers) Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org> Reviewed-by: Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com> Tested-by: Cornelia Huck <cohuck@redhat.com> # running tests on an s390x Message-ID: <20260601143129.144786-4-alex.bennee@linaro.org> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>