The editor seems to knows where the class is because the "Go to Definition" function works but for some reason there is a disconnect with the PHP tool.
I added a use statement for the class, but then it complained that the use statement didn't do anything and was unnecessary. So I'm not really sure what to do about it.
The code also works so it can find the class.
The issue is in a config file where the a constant from the Redis class is being referenced as the default to an env var in the helper function env('SOME_ENV_VAR', Redis::SOME_CONSTANT)