De-compact async with tuple on 3.8-

Turns out can't use the nicer syntax before python 3.9 (even though it
doesn't seem documented anywhere?).

Relates to #207

examples/full_fledged_streaming_service.py

@@ -29,10 +29,10 @@ async def aggregate(seed):
         send_chan, recv_chan = trio.open_memory_channel(500)
 
         async def push_to_chan(portal, send_chan):
-            async with (
-                send_chan,
-                portal.open_stream_from(stream_data, seed=seed) as stream,
-            ):
+
+            # TODO: https://github.com/goodboy/tractor/issues/207
+            async with send_chan:
+                async with portal.open_stream_from(stream_data, seed=seed) as stream:
                     async for value in stream:
                         # leverage trio's built-in backpressure
                         await send_chan.send(value)

tests/test_discovery.py

@@ -268,10 +268,12 @@ async def close_chans_before_nursery(
                 portal2 = await tn.start_actor(
                     'consumer2', enable_modules=[__name__])
 
-                async with (
-                    portal1.open_stream_from(stream_forever) as agen1,
-                    portal2.open_stream_from(stream_forever) as agen2,
-                ):
+                # TODO: compact this back as was in last commit once
+                # 3.9+, see https://github.com/goodboy/tractor/issues/207
+                async with portal1.open_stream_from(stream_forever) as agen1:
+                    async with portal2.open_stream_from(
+                        stream_forever
+                    ) as agen2:
                         async with trio.open_nursery() as n:
                             n.start_soon(streamer, agen1)
                             n.start_soon(cancel, use_signal, .5)

tests/test_pubsub.py

@@ -60,14 +60,13 @@ async def subs(
         def pred(i):
             return isinstance(i, int)
 
+    # TODO: https://github.com/goodboy/tractor/issues/207
     async with tractor.find_actor(pub_actor_name) as portal:
-        async with (
-            portal.open_stream_from(
+        async with portal.open_stream_from(
             pubber,
             topics=which,
             seed=seed,
-            ) as stream
-        ):
+        ) as stream:
             task_status.started(stream)
             times = 10
             count = 0
@@ -81,13 +80,11 @@ async def subs(
 
             await stream.aclose()
 
-        async with (
-            portal.open_stream_from(
+        async with portal.open_stream_from(
             pubber,
             topics=['odd'],
             seed=seed,
-            ) as stream
-        ):
+        ) as stream:
             await stream.__anext__()
             count = 0
             # async with aclosing(stream) as stream: