Ensure `RedisIntegration` is disabled, unless `redis` is installed #3071

Job	Run time
huey, python 3.5, ubuntu-20.04	57s
huey, python 2.7, ubuntu-20.04	1m 2s
huey, python 3.6, ubuntu-20.04	49s
huey, python 3.7, ubuntu-20.04	49s
huey, python 3.8, ubuntu-20.04	45s
huey, python 3.9, ubuntu-20.04	47s
huey, python 3.10, ubuntu-20.04	43s
huey, python 3.11, ubuntu-20.04	44s
huey, python 3.12, ubuntu-20.04	55s
All huey tests passed or skipped	1s
	7m 32s

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