allow templating of ansible_ssh_private_key_file also in the synchronize module

lib/ansible/runner/action_plugins/synchronize.py

@@ -135,6 +135,8 @@ class ActionModule(object):
             else:
                 private_key = inject.get('ansible_ssh_private_key_file', self.runner.private_key_file)
 
+            private_key = template.template(self.runner.basedir, private_key, inject, fail_on_undefined=True)
+
             if not private_key is None:
                 private_key = os.path.expanduser(private_key)
                 options['private_key'] = private_key