Return 404 when rendering Repositories#Archive as HTML

What does this MR do?

Currently, if you try to download a repository archive with a direct URL, but have a typo in the URL or are missing the format (.zip, etc), you get a 500 error. These have shown up in Google SEO as a negative impact.

If you navigate to, for example, https://gitlab.com/gitlab-org/gitlab/-/archive/master/gitlab-master or https://gitlab.com/gitlab-org/gitlab/-/archive/master/gitlab-master.zip"" the request is rendered as HTML. This MR will prevent those accessing archive downloads via HTML and return a 404 to them instead.

Closes: #199366 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team