Node provision fails with the error expected token 'end of print statement', got '_mtu'

Environment

• Running openstack overcloud node provision command fails in rendering process of network_config.

FATAL | Render network_config from template | controller-0 | error={"changed": false, "msg": "AnsibleError: template error while templating string: expected token 'end of print statement', got '_mtu'.

• In the overcloud-baremetal-deploy.yaml file used for openstack overcloud node provision, a NIC template is used in network_config, and the {{ XXXX }} is used within the Jinja2 template.

mtu: {{ external-1_mtu }}