Non-annotated tags do not seem to work when generating the changelog

If a non-annotated tag is created (such as without `-a` or `-s`) and `generate` is used, the changelog generator cannot retrieve the object for the previous release and cannot generate the changelog.

Start with the generate command and reproduce the failure using a non-annotated tag created without -a or -s. Trace how the previous release object is retrieved, then verify that generate produces the changelog successfully for non-annotated tags.

Written by the indexing model from the issue text.