chore(deps): update redis docker tag to v8

# so this augments the base job (and is inherited by anything that extends it).

rspec:

  services:

    - name: redis:7-alpine

    - name: redis:8-alpine

      alias: redis

  variables:

    LABKIT_TEST_REDIS_URL: redis://redis

services:

  redis:

    image: redis:7-alpine

    image: redis:8-alpine

    ports:

      - "6390:6379"

    healthcheck: