fix: ssh not using correct identity

modules/capabilities/git.nix

@@ -32,6 +32,7 @@ in
             };
           }
           // lib.optionalAttrs hasSigningKey {
+            core.sshCommand = "ssh -i ${privateKeyPath} -o IdentitiesOnly=yes";
             gpg.ssh.allowedSignersFile = allowedSignersFile;
           };
         };