Can not install Redis-Py v4.1.0 in Alpine Linux 3.15

[rashley-iqt]

Thanks for wanting to report an issue you've found in redis-py. Please delete this text and fill in the template below.
It is of course not always possible to reduce your code to a small test case, but it's highly appreciated to have as much data as possible. Thank you!

Version: What redis-py and what redis version is the issue happening on?
Redis-Py v4.1.0 and Redis 6.2.6

Platform: What platform / version? (For example Python 3.5.1 on Windows 7 / Ubuntu 15.10 / Azure)
Python 3.9.7-r4 on Alpine Linux 3.15 in Docker

Description: Description of your issue, stack traces from errors and code that reproduces the issue
Error Message:

Attempting uninstall: packaging
    Found existing installation: packaging 20.9
ERROR: Cannot uninstall 'packaging'. It is a distutils installed project and thus we cannot accurately determine which files belong to it which would lead to only a partial uninstall.

The requirements.txt file does not specify a version for the dependency on packaging and is implicitly defaulting to latest. this prevents installation in environments where packaging has been installed as part of the OS

To reproduce:

1. clone this repo
2. git checkout renovate/redis-4.x
3. cd into the web directory
4. docker build .

[chayim]

This change: 1fc1233 should solve part of the issue.

However I've added a PR to close this off from the requirements.txt side as well.