[pip 20.3](https://pip.pypa.io/en/stable/news/) just got released and sets its new resolver as default.
However it does not seem stable enough yet as the pip command to install swh
dependencies now ends up executing a really long package [backtracking](https://pip.pypa.io/en/stable/user_guide/#dependency-resolution-backtracking) process
that makes the swh-environment Jenkins job timeout.
Until this got sorted out by pip developers (https://github.com/pypa/pip/issues/9187), workaround the issue by splitting
out the pip command into multiple ones (one by swh package).