Fix Error 500 when repositories contain annotated tags pointing to blobs
In repositories such as https://github.com/git/git.git, annotated tags can
point to blobs, not necessarily to commits. Repository
attempts to
return the tags in the order of the commit date, but if a commit is not
available the previous implementation would error due to a nil
target.
This change modifies the code to use the current time if a commit
is not associated with the given tag.
Closes #27228 (closed)