Update redis/redis-rb from 4.8.0 to 5.0.5

The following dependencies have been updated by deps:

Update gitlab-mailroom's use of redis/redis-rb gem from 4.8.0 to 5.0.5

• Major versions changes can be found at https://github.com/redis/redis-rb/blob/master/CHANGELOG.md#500
• Patch versions changes can be found at https://github.com/redis/redis-rb/blob/master/CHANGELOG.md#505