ci: Bump lint imagefile FROM base

According to https://wiki.debian.org/DebianReleases#Production_Releases,
the current image will be EOL in about one year, so it seems fine to
slowly bump it to something more recent.

Author: MarcoFalke

ci/lint_imagefile

@@ -4,7 +4,7 @@
 
 # See test/lint/README.md for usage.
 
-FROM mirror.gcr.io/debian:bookworm
+FROM mirror.gcr.io/ubuntu:24.04
 
 ENV DEBIAN_FRONTEND=noninteractive
 ENV LC_ALL=C.UTF-8