Some time ago, it was discovered that Git archives having
`ref-names: $Format:%D$` in `.git_archival.txt` may change when
references existing in the repository change over time [[1]]. This
means that downloading an archive for a commit from an immutable URL
may start yielding slightly different results. This hurts the ability
of downstreams to source projects from Git archive URLs.
With that in mind, modern `setuptools-scm` advises against having this
entry in the `.git_archival.txt` template [[2]]. And this patch
implements said recommendation.
[1]: https://github.com/pypa/setuptools_scm/issues/806
[2]: https://setuptools-scm.readthedocs.io/en/latest/usage/#git-archives
This patch enables the end-users to succeed installing from GitHub
source Git archive URLs, letting `setuptools-scm` calculate the
distribution version correctly, including the exports of non-tagged
commits[1].
[1] https://github.com/pypa/setuptools_scm#git-archives
Sviatoslav Sydorenko (Святослав Сидоренко)