bootc install to-existing-root randomly failed on s390x due to zipl not found

On IBM s390x VM instance with package mode RHEL, convert to image mode with the following command will 100% PASS (run 10 time)
```
podman run --rm --privileged --pid=host --security-opt label=type:unconfined_t -v /:/target -v /dev:/dev -v /var/lib/containers:/var/lib/containers quay.io/centos-bootc/centos-bootc:strea
m10 bootc install to-existing-root --acknowledge-destructive
```
But it has a >50% chance of failing (17 out of 30) with the following command (compare to the cmd above, this one only add `-v /root/.ssh:/output`)
```
podman run --rm --privileged --pid=host --security-opt label=type:unconfined_t -v /:/target -v /dev:/dev -v /var/lib/containers:/var/lib/containers -v /root/.ssh:/output quay.io/centos-boo
tc/centos-bootc:stream10 bootc install to-existing-root --acknowledge-destructive
```
and the error output is
```
Installing image: docker://quay.io/centos-bootc/centos-bootc:stream10
Digest: sha256:a084b73d846ef83ec123a506a74205dc1d2e1b0535dec67686a382bb5edeba7e
Installing to `dos` format partitions is not recommended
Reusing extant ostree layout
Deploying container image...done (7 seconds)
error: Installing to filesystem: Installing bootloader using zipl: No such file or directory (os error 2)
```
To reproduce on a IBM cloud s390x VM, you can use testing-farm RH ranch(will failover to beaker if hit capacity issues)
```
testing-farm reserve --arch s390x --compose RHEL-10.1-Nightly
```