Bump gemnasium-python, bundler-audit, and gemnasium-maven versions

What does this MR do?

This MR bumps the version of:

• gemnasium-python (to v2.6.0)
• gemnasium-maven (to v2.6.0)
• bundler-audit (to v2.2.0)

What are the relevant issue numbers?

• gitlab-org/gitlab#12811 (closed)
• gitlab-org/gitlab#8524 (closed)
• gitlab-org/gitlab#12390 (closed)
• gitlab-org/gitlab#33718 (closed)

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
  • [-] Job definition example
  • [-] CI Templates (to be removed)
  • [-] Vendored CI Templates (also in CE)
  • [-] Ensure that all of the ENV vars supported are propagated to Docker containers upon docker run in job definitions
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer