Description of problem:
Installing / upgrading kernel in kickstart post installation script creates a boot entry without root set and with the wrong kernel cmdline arguments such that the entry boots into the emergency shell

Version-Release number of selected component (if applicable):
s390utils-core-2.22.0-2.el9.s390x

How reproducible:
always

Steps to Reproduce:
1. Add another kernel / installation repo in %post
2. dnf install -y kernel in %post

Actual results:
root= is not set, kernel cmdline arguments passed to new kernel come from installation (/proc/cmdline)
Machine reboots to emergency shell

Expected results:
root and cmdline arguments are set correctly and machine boots new kernel

Additional info:
This was fixed incidentally on all others arches that use grub2 as a bootloader:
https://bugzilla.redhat.com/show_bug.cgi?id=1940288
rharwood has already opened a PR which should fix this issue: https://src.fedoraproject.org/rpms/s390utils/pull-request/5
This is a high priority bug which customers are waiting for and will need to be quickly backported to RHEL 9.0