Transform inline sample-folder into archive and adapt fixture accordingly

Since the setuptools-scm migration, the build fails because the sample-folder within the repository held symlinks which setuptools-scm does not deal with properly.

This adapts the conftest fixture to deal with the transformation from folder to an archive (still holding the symlinks).

This fixes the build [1]

• [1] https://jenkins.softwareheritage.org/job/DTSCN/job/tests/194/console

Related to swh-environment#2105 (closed)

Test Plan

tox

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Migrated from D3720 (view on Phabricator)