Change: honor RESTIC_CACHE_DIR environment variable in the check command

--cache-dir option doesn't honor the RESTIC_CACHE_DIR environment variable by
default. This fixes an issue with the restic check command that doesn't obey the
RESTIC_CACHE_DIR environment variable. Extend the behavior of cache command to
manage directories created by restic check.

https://github.com/restic/restic/issues/3382
https://github.com/restic/restic/pull/3474