Python to 3.8.6

What does this MR do?

Upgrade Python to 3.8.6

Closes https://gitlab.com/gitlab-org/charts/gitlab/-/issues/2538

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com