Update redis-py dependency to >=4.5.3.

For https://github.com/redis/redis-py/releases/tag/v4.5.3

Author: carltongibson

setup.py

@@ -31,7 +31,7 @@
     include_package_data=True,
     python_requires=">=3.7",
     install_requires=[
-        "redis==4.3.5",
+        "redis>=4.5.3",
         "msgpack~=1.0",
         "asgiref>=3.2.10,<4",
         "channels",