ci: Freeze pipenv version for avoiding issue on documentation generation

[gustavonihei]

Summary

This PR intends to add a quick fix for an issue with the latest release of pipenv.

From my investigation seems related to this issue: pypa/pipenv#4828

Impact

No impact, fix for CI job.

Testing

CI build pass.

[Ouss4]

So what's the root cause? I had some desperate attempts locally. OK I see the updated description.

[gustavonihei]

So what's the root cause? I had some desperate attempts locally.

It seems that pipenv run is failing to actually execute the command inside the virtual environment.
The alternative method works: running make run html inside pipenv shell.

[Ouss4]

It looks like there is a fix for this already but still not part of any release, we'll have to merge this then.

[gustavonihei]

It looks like there is a fix for this already but still not part of any release, we'll have to merge this then.

Just for future reference, the fix is already merged upstream:
pypa/pipenv#4838

Once the hotfix is published to pypi, we can unfreeze pipenv version by reverting this commit.