outposts: fix formatting of image name

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

authentik/outposts/controllers/base.py

@@ -61,6 +61,4 @@ class BaseController:
     def get_container_image(self) -> str:
         """Get container image to use for this outpost"""
         image_name_template: str = CONFIG.y("outposts.docker_image_base")
-        return image_name_template.format(
-            {"type": self.outpost.type, "version": __version__}
-        )
+        return image_name_template % {"type": self.outpost.type, "version": __version__}