Schema validation fails on jinja template

This bug was originally filed in Launchpad as [LP: #1881925](https://bugs.launchpad.net/cloud-init/+bug/1881925)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2020-06-03T14:57:36.281765+00:00

date_fix_committed = None

date_fix_released = None

id = 1881925

importance = medium

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1881925

milestone = None

owner = falcojr

owner_name = James Falcon

private = False

status = in_progress

submitter = falcojr

submitter_name = James Falcon

tags = []

duplicates = []

_Launchpad user **James Falcon(falcojr)** wrote on 2020-06-03T14:57:36.281765+00:00_

$ cat > test.yaml << EOF
## template: jinja
#cloud-config
runcmd:
- echo 'hostname: {{ ds.meta_data.public_hostname }}'

EOF
$ cloud-init devel schema -c test.yaml
Cloud config schema errors: format-l1.c1: File test.yaml needs to begin with "#cloud-config"