custom subdomain false positive warning

I get this warning on every check in to https://github.com/Possum-Labs/DSL/tree/master/docs

“Your site’s DNS settings are using a custom subdomain, dsl.possumlabs.com, that’s set up as an A record. We recommend you change this to a CNAME record pointing at Possum-Labs.github.io. For more information, see https://help.github.com/en/github/working-with-github-pages/configuring-a-custom-domain-for-your-github-pages-site.”

There is no wildcard set up.

http://possumlabs.com/ is served from
https://github.com/Possum-Labs/Homepage

http://dsl.possumlabs.com/ is served from
https://github.com/Possum-Labs/DSL/tree/master/docs

everything works as expected, and I hope to add more tools with more subdomains as I continue migrating projects into this new structure.

Is there a way to turn this warning off?