Fix docs markup for asyncio current_task() and all_tasks() (GH-6089)

(cherry picked from commit b21505e)

Co-authored-by: Andrew Svetlov <[email protected]>

Author: miss-islington

Doc/library/asyncio-task.rst

@@ -535,7 +535,7 @@ Task functions
    not provided, the default event loop is used.
 
 
-.. function:: current_task(loop=None):
+.. function:: current_task(loop=None)
 
    Return the current running :class:`Task` instance or ``None``, if
    no task is running.
@@ -546,7 +546,7 @@ Task functions
    .. versionadded:: 3.7
 
 
-.. function:: all_tasks(loop=None):
+.. function:: all_tasks(loop=None)
 
    Return a set of :class:`Task` objects created for the loop.