sphinx-dev job: Use git clone --single-branch instead of --depth 1
Using --depth makes git describe
return nonsensical values, which in
turn makes setuptools-scm generate a v0.1.dev1 version number. This
makes pip unable to resolve version-constrained dependencies on swh
modules, which makes it install them from pip again.
Test Plan
it works in prod™
Migrated from D7737 (view on Phabricator)