Update stale links in DS docs

What does this MR do and why?

Now that Remove code (moved to gemnasium project) (gitlab-org/security-products/analyzers/gemnasium-maven!195 - merged) and Remove code (moved to gemnasium project) (gitlab-org/security-products/analyzers/gemnasium-python!179 - merged) have been merged, and all related code has been moved to the gemnasium project, we need to update the links in the Dependency Scanning documentation to reference the new test locations, which is what this MR does.

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