Removing python 3.8 from build image

What does this MR do?

This MR removes Python 3.8 from the mobsf built image based on the justification listed in the issue below

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab/-/issues/336134

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer