Revert "Upgrade Docker images to Ubuntu 23.10" on sparc64

This partially reverts commit 946c348.

The test binaries were getting a symbol version for `GLIBC_2.38`, but
the debian-11 image used for qemu doesn't have that new of glibc.

ci/docker/sparc64-unknown-linux-gnu/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:23.10
+FROM ubuntu:22.04
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         curl ca-certificates \