ci: roll back the version of checkout for "build (compat, ubuntu:18.04)"

ci: roll back the version of checkout for "build (compat, ubuntu:18.04)"

With the change 28af8ed133ff15d50b5e2d644c6617d0a3e17033, we got the
following error at "Post repository checkout" stage on "build (compat, ubuntu:18.04)":

  Post job cleanup.
  /usr/bin/docker exec  94db032be2efb37ea68b3ce562ce52ba3dea047f5ac970aabb7fded075116c20 sh -c "cat /etc/*release | grep ^ID"
  /__e/node20/bin/node: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.28' not found (required by /__e/node20/bin/node)

Signed-off-by: Masatake YAMATO <yamato@redhat.com>