hirsute s390x kernel upgrade reports placeholder

I was upgrading Hirsute to hirsute-proposed and got this text:

"
Pending kernel upgrade
Newer kernel available
The currently running kernel version is 5.11.0-17-generic which is not the expected kernel version %s.
Restarting the system to load the new kernel will not be handled automatically, so you should consider rebooting.
"

One would expect the %s to be replaced, but it isn't

The new kernel was:
Processing triggers for linux-image-5.11.0-18-generic (5.11.0-18.19) ...
/etc/kernel/postinst.d/initramfs-tools:
update-initramfs: Generating /boot/initrd.img-5.11.0-18-generic

I don't know if this is a s390x-kernel (not having the right data set) or a needrestart (fail to probe version on s390x) issue so I'm filing it against both.

Repro:
1. get a s390x system (KVM guest is fine, no need for an LPAR)
2. install hirsute
3. upgrade the kernel
---
ProblemType: Bug
AlsaDevices: Error: command ['ls', '-l', '/dev/snd/'] failed with exit code 2: ls: cannot access '/dev/snd/': No such file or directory
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.20.11-0ubuntu65
Architecture: s390x
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
CRDA: N/A
CasperMD5CheckResult: unknown
DistroRelease: Ubuntu 21.04
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
Lspci:

Lspci-vt: -[0000:00]-
Lsusb: Error: command ['lsusb'] failed with exit code 1:
Lsusb-t: Error: command ['lsusb', '-t'] failed with exit code 1: /sys/bus/usb/devices: No such file or directory
Lsusb-v: Error: command ['lsusb', '-v'] failed with exit code 1:
Package: needrestart 3.5-2ubuntu2
PackageArchitecture: all
PciMultimedia:

ProcFB:

ProcKernelCmdLine: root=LABEL=cloudimg-rootfs
ProcVersionSignature: Ubuntu 5.11.0-18.19-generic 5.11.17
RelatedPackageVersions:
 linux-restricted-modules-5.11.0-18-generic N/A
 linux-backports-modules-5.11.0-18-generic N/A
 linux-firmware N/A
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
Tags: hirsute uec-images
Uname: Linux 5.11.0-18-generic s390x
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: N/A
_MarkForUpload: True
acpidump: