Fix typo (GH-12878)

"sychronization" -> "synchronization"
(cherry picked from commit 3e986de)

Co-authored-by: Fredrik Averpil <fredrik@averpil.com>

Doc/library/asyncio-sync.rst

@@ -17,7 +17,7 @@ those of the :mod:`threading` module with two important caveats:
   argument; use the :func:`asyncio.wait_for` function to perform
   operations with timeouts.
 
-asyncio has the following basic sychronization primitives:
+asyncio has the following basic synchronization primitives:
 
 * :class:`Lock`
 * :class:`Event`