Fix issue with Python importlib_metadata requirements when building Dockerfile.base

[giogix2]

This PR fixes the following issue #1293.
In particular, when building the docker, the following error is thrown
AttributeError: module 'importlib_metadata' has no attribute 'EntryPoints'
This solution was suggested in this this Stackoverflow post.

[lanctot]

Thank you!

[lanctot]

Same here please: Can you pull changes from master and push the merge commit to trigger the CI tests again?

[giogix2]

Let me know if this one is failing because of my change. I guess it's not the case, as from what I understand this Dockerfile is not tested in the CI/CD. I was wondering whether it's still the same issue as lat time, but the other to PRs have worked after the latest changes 🤔.

[lanctot]

Oh, that file_test periodically fails.. I'm never sure why, it's non-deterministic (maybe a race condition).

So yes, certainly not due to your PR. I've restarted the CI tests. Maybe I can file an issue to remind us to fix it.