I added my gpg subkey to GitHub today and noticed that regardless of which subkey I export, the PUBLIC KEY BLOCK is the same. I have since found this post, that explains why: is-it-possible-to-export-a-gpg-subkeys-public-component?
In adding this public key block to github, it has now recognised my public key, and lists both my encryption and signing subkeys under my account.
My question then, is how do I know which key github is using for signing, since my public key has usage
SC, and my signing key has usage