Revert "[hotfix] interim fix to get docker-build of CI without issues"

This reverts interim fix from commit 50c4b58d and adds requirement
`redis==4.1.1`.

The interim fix was needed by Alpine images (Docker) [1] and has been fixed in
commit [2] merged with the patch series from [3].  In redis-py version 4.1.1
this pach has been released on PyPi [4].

[1] https://github.com/redis/redis-py/issues/1869
[2] https://github.com/redis/redis-py/commit/1fc1233f
[3] https://github.com/redis/redis-py/pull/1854
[4] https://github.com/redis/redis-py/issues/1880



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>