**Description** <!--What needs to be improved? What should be done? Has there been any related work before? Any relevant links or material? --> #542 added support for TUF "bundled" trust roots. We need tests to cover the new surface, namely: - [x] the `get` methods - [x] `get_rekor_keys` - [x] `get_fulcio_certs` - [x] `get_ctfe_keys` - [ ] `_get_trusted_root`
