Unable to deploy CentOS subordinate charm from charmhub

[Heitor]

```
$ juju deploy fluentbit --channel latest/edge --series centos7
ERROR series "centos7" not supported by charm, supported series are: panther,focal. Use --force to deploy the charm anyway.
```

What is this `panther` series? And why Juju can't deploy this charm on CentOS7, even though the charm supports it? https://charmhub.io/fluentbit

We can deploy other CentOS charms, but this one and prometheus-node-exporter give us this weird error message. Maybe because they are subordinate charms?

The only reference I got for panther in Juju source code is in core/series supported.go:536, but it shows as macOSXSeries version 7...

I also see this error message when deploying these charms from a local file.

Juju 2.9.17