`openshift-install agent create image` fails with error: `nmstate only support saving DNS to interface with static gateway or auto interface with auto-dns:false`

Issue

When executing openshift-install agent create image under the following environment, an error nmstate only support saving DNS to interface with static gateway or auto interface with auto-dns:false is displayed, and the ISO file is not generated:

• RHEL8/nmstatectl 1.x
• agent-config.yaml written for deployment on a Disconnected Network without a default gateway.

ERROR <nmstatectl gc> failed, errorCode 1, stderr Traceback (most recent call last):  pkg=manifests
ERROR   File "/usr/bin/nmstatectl", line 11, in <module>  pkg=manifests
ERROR     load_entry_point('nmstate==1.4.4', 'console_scripts', 'nmstatectl')()  pkg=manifests
ERROR   File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 74, in main  pkg=manifests
ERROR     return args.func(args)                    pkg=manifests
ERROR   File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 397, in run_gen_config  pkg=manifests
ERROR     libnmstate.generate_configurations(state), use_yaml=use_yaml  pkg=manifests
ERROR   File "/usr/lib/python3.6/site-packages/libnmstate/nmstate.py", line 429, in generate_configurations  pkg=manifests
ERROR     net_state = NetState(desire_state, gen_conf_mode=True)  pkg=manifests
ERROR   File "/usr/lib/python3.6/site-packages/libnmstate/net_state.py", line 88, in __init__  pkg=manifests
ERROR     raise e                                   pkg=manifests
ERROR   File "/usr/lib/python3.6/site-packages/libnmstate/net_state.py", line 84, in __init__  pkg=manifests
ERROR     self._dns, self._route, ignored_dns_ifaces  pkg=manifests
ERROR   File "/usr/lib/python3.6/site-packages/libnmstate/ifaces/ifaces.py", line 815, in gen_dns_metadata  pkg=manifests
ERROR     self, route_state, ignored_dns_ifaces     pkg=manifests
ERROR   File "/usr/lib/python3.6/site-packages/libnmstate/dns.py", line 122, in gen_metadata  pkg=manifests
ERROR     "auto-dns:false" % server                 pkg=manifests
ERROR libnmstate.error.NmstateValueError: Failed to find suitable interface for saving DNS name servers: 10.21.0.1, nmstate only support saving DNS to interface with static gateway or auto interface with auto-dns:false  pkg=manifests
ERROR , input yaml <dns-resolver:                   pkg=manifests
ERROR   config:                                     pkg=manifests
ERROR     server:                                   pkg=manifests
ERROR     - 10.21.0.1                               pkg=manifests
ERROR interfaces:                                   pkg=manifests
ERROR - ipv4:                                       pkg=manifests
ERROR     address:                                  pkg=manifests
ERROR     - ip: 10.21.0.80                          pkg=manifests
ERROR       prefix-length: 23                       pkg=manifests
ERROR     dhcp: false                               pkg=manifests
ERROR     enabled: true                             pkg=manifests
ERROR   mac-address: 52:54:00:65:61:21              pkg=manifests
ERROR   name: enp1s0                                pkg=manifests
ERROR   state: up                                   pkg=manifests
ERROR   type: ethernet                              pkg=manifests
ERROR >                                             pkg=manifests
ERROR failed to write asset (Agent Installer ISO) to disk: cannot generate ISO image due to configuration errors 
FATAL failed to fetch Agent Installer ISO: failed to fetch dependency of "Agent Installer ISO": failed to fetch dependency of "Agent Installer Ignition": failed to fetch dependency of "Agent Manifests": failed to generate asset "NMState Config": staticNetwork configuration is not valid: 1 error occurred: 
FATAL     * failed to validate network yaml for host 0, failed to execute 'nmstatectl gc', error: Failed to find suitable interface for saving DNS name servers: 10.21.0.1, nmstate only support saving DNS to interface with static gateway or auto interface with auto-dns:false 
FATAL                                              
FATAL