Configuring git to use SSH (a little misleading calling it gpg.format) for signing commits:
git config --global gpg.format ssh
Configuring git to sign commits with your SSH key:
git config --global user.signingkey $env:USERPROFILE\.ssh\id_ed25519.pub
git config --global gpg.ssh.allowedSignersFile $env:USERPROFILE\.ssh\allowed_signers