Bump Python to 3.8.4

What does this MR do?

Bump Python to 3.8.4

Closes https://gitlab.com/gitlab-org/charts/gitlab/-/issues/2477

Closes https://gitlab.com/gitlab-org/charts/gitlab/-/issues/2478

Closes https://gitlab.com/gitlab-org/charts/gitlab/-/issues/2479

Testing

helm install XYZ gitlab/gitlab --set global.gitlabVersion=python-3-8-4

Checklist

See Definition of done.

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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

Expected (please provide an explanation if not completing)

• The impact any change in container size has should be evaluated