Use non-standard named ssh keys with github

I was getting (publickey denied) when trying to push to GH using ssh. When I tested the connection I saw that a bunch of keys in ``~/.ssh/ were being attempted

✗ ssh [email protected] -vv

...

debug1: Will attempt key: /home/nic/.ssh/id_rsa 
debug1: Will attempt key: /home/nic/.ssh/id_ecdsa 
debug1: Will attempt key: /home/nic/.ssh/id_ecdsa_sk 
debug1: Will attempt key: /home/nic/.ssh/id_ed25519 
debug1: Will attempt key: /home/nic/.ssh/id_ed25519_sk 
debug1: Will attempt key: /home/nic/.ssh/id_xmss 
debug1: Will attempt key: /home/nic/.ssh/id_dsa 

...

debug1: No more authentication methods to try.
[email protected]: Permission denied (publickey).

None of those were the key I setup with GH. So I added an entry into ~/.ssh/config:

Host
github.com
User git
Port 22
Hostname github.com
IdentityFile ~/.ssh/my_custom_github_key
TCPKeepAlive yes
IdentitiesOnly yes