docs: Add timeout parameter for get_message example (#3129)

The `get_message()` method in asyncio PubSub has a `timeout` argument that defaults to 0.0, causing it to immediately return. This can cause high CPU usage with the given code example and should not be recommended. By setting `timeout=None`, it works with much more efficient resource usage.

Author: hongqn

docs/examples/asyncio_examples.ipynb

@@ -201,7 +201,7 @@
     "\n",
     "async def reader(channel: redis.client.PubSub):\n",
     "    while True:\n",
-    "        message = await channel.get_message(ignore_subscribe_messages=True)\n",
+    "        message = await channel.get_message(ignore_subscribe_messages=True, timeout=None)\n",
     "        if message is not None:\n",
     "            print(f\"(Reader) Message Received: {message}\")\n",
     "            if message[\"data\"].decode() == STOPWORD:\n",
@@ -264,7 +264,7 @@
     "\n",
     "async def reader(channel: redis.client.PubSub):\n",
     "    while True:\n",
-    "        message = await channel.get_message(ignore_subscribe_messages=True)\n",
+    "        message = await channel.get_message(ignore_subscribe_messages=True, timeout=None)\n",
     "        if message is not None:\n",
     "            print(f\"(Reader) Message Received: {message}\")\n",
     "            if message[\"data\"].decode() == STOPWORD:\n",