If the goal is to be able to push to a GitHub repo whenever you want to, then in Windows under C:\Users\tiago\.ssh
where the keys are stored (at least in my case), create a file named config and add the following in it
Host github.com
HostName github.com
User your_user_name
IdentityFile ~/.ssh/your_file_name
Then simply open Git Bash and you'll be able to push without having to manually start the ssh-agent and adding the key.