Regression: TUF contents are not saved to disk anymore

[flavio]

Description

Up to version 0.7.2, the SigstoreRepository::fetch method took care of synchronizing the contents of a local checkout of Sigstore's TUF repository.

Now (v0.8.0 being latest stable release), the SigstoreTrustRoot::new method tries to take advantage of a local cache of the TUF repository, but it doesn't update the local contents.

The code that takes care of synchronizing the local cache is still part of the sigstore-rs codebase, but it's no longer being used.

[tnytown]

Apologies for the regression. #311 reworks the target fetching functionality and caches the trust root correctly.

[flavio]

@tnytown no worries, ping me on the other PR when it's ready to be reviewed

[flavio]

Closing, this has been fixed