MOTOR-1214 Ignore IOLoop.current deprecation to make synchro pass (#236)

synchro/__init__.py

@@ -22,6 +22,7 @@ DO NOT USE THIS MODULE.
 import functools
 import inspect
 import unittest
+import warnings
 from typing import Generic, TypeVar
 
 # Make e.g. "from pymongo.errors import AutoReconnect" work. Note that
@@ -337,7 +338,9 @@ class Synchro(metaclass=SynchroMeta):
             def partial():
                 return async_method(*args, **kwargs)
 
-            return IOLoop.current().run_sync(partial)
+            with warnings.catch_warnings(action="ignore", category=DeprecationWarning):
+                loop = IOLoop.current()
+            return loop.run_sync(partial)
 
         return synchronized_method