Enhancement: Make `check` command create non-existent cache directory

Previously, if a custom cache directory was specified for the `check` command,
but the directory did not exist, `check` continued with the cache disabled.

The `check` command now attempts to create the cache directory before
initializing the cache.

https://github.com/restic/restic/issues/4437
https://github.com/restic/restic/pull/4805
https://github.com/restic/restic/pull/4883
