secure-fetch does not save fetched tags.

[gchronis]

While doing some acceptance testing for git-promote, I keep failing on the merge step. The script acts like the pre-release tag is successfully fetched, but then fails on the merge step (i.e. merging devel tag into release branch), complaining that ERROR: merge: v1 - not something we can merge. The problem stems from fetching tags by name rather than all at once.
By name (v1 is a remote tag):

gchronis@gchronis:~/dotfiles$ git fetch origin v1
From github.com:gchronis/dotfiles
 * tag               v1         -> FETCH_HEAD
gchronis@gchronis:~/dotfiles$ git tag   
gchronis@gchronis:~/dotfiles$

All at once:

gchronis@gchronis:~/dotfiles$ git fetch --tags
From github.com:gchronis/dotfiles
 * [new tag]         v1         -> v1
gchronis@gchronis:~/dotfiles$ git tag
v1

We need to fetch tags by explicitly by name in order to ensure that their fetch and push histories are recorded in the RSL. The problem is that fetching tags by name doesn't create a local ref automatically, they way fetching branches does. We will need to create a reference to the FETCH_HEAD, possibly using one of the strategies listed here https://stackoverflow.com/questions/45338495/fetch-a-single-tag-from-remote-repository.