Enhancement: `check` command creates cache directory if it does not exist

If a custom cache directory was specified for the `check` command but the directory did not exist,
then `check` continued with 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