coreos-base/oem-ec2-compat: fix JSON formatting

[tormath1]

It was causing an issue on AWS for both arch:

$ aws ec2 get-console-output
[    8.130342] ignition[1051]: Ignition 2.15.0
[    8.131688] ignition[1051]: Stage: fetch-offline
[    8.134886] ignition[1051]: reading system config file "/usr/lib/ignition/base.d/base.ign"
[    8.137355] ignition[1051]: error at line 16 col 6: invalid character ']' looking for beginning of value
[    8.139947] ignition[1051]: failed to acquire system base config: config is not valid
[    8.142090] ignition[1051]: Ignition failed: config is not valid
[    8.145266] systemd[1]: ignition-fetch-offline.service: Main process exited, code=exited, status=1/FAILURE
[    8.147987] systemd[1]: ignition-fetch-offline.service: Failed with result 'exit-code'.
[    8.150262] systemd[1]: Failed to start ignition-fetch-offline.service - Ignition (fetch-offline).
$ ./ign-converter < base.ign
error at line 16, column 6
   15:       },
   16:     ]
           ^
invalid character ']' looking for beginning of valueError parsing spec v2 config: config is not valid
error at line 16, column 6
   15:       },
   16:     ]
           ^
invalid character ']' looking for beginning of value
$ jq < base.ign
jq: parse error: Expected another array element at line 16, column 5

---

Tested with jq only.

[tormath1]

cherry-picked to:

• flatcar-3637

[github-actions]

Build action triggered: https://github.com/flatcar/scripts/actions/runs/5323189233