[Backport] Go-get: return 404 error code when personal token is invalid

What does this MR do and why?

Contributes to #501082 (closed)

Problem

When user provides an invalid personal access token with credentials and authentication by password is not supported, then GitLab responds with 401 error code instead of an expected code 404.

Solution

Return 404 error code to make responses for invalid credentials case consistent.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch. See !170831 (merged)
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:test-on-omnibus-ee job has either succeeded or been approved by a Software Engineer in Test.

Note to the merge request author and maintainer

If you have questions about the patch release process, please:

• Refer to the patch release runbook for engineers and maintainers for guidance.
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