[tasks] make __call__ actually appear in the docs

discord/ext/tasks/__init__.py

@@ -161,7 +161,7 @@ class Loop:
         return self._next_iteration
 
     async def __call__(self, *args, **kwargs):
-        """|coro|
+        r"""|coro|
 
         Calls the internal callback that the task holds.
 

docs/ext/tasks/index.rst

@@ -139,5 +139,6 @@ API Reference
 
 .. autoclass:: discord.ext.tasks.Loop()
     :members:
+    :special-members: __call__
 
 .. autofunction:: discord.ext.tasks.loop