Evidence - Added restriction for guest on Release page

What does this MR do?

On the Release page, project guests cannot download code source when the project is private. The same restriction should also be applied to evidence data (both evidence sha and evidence JSON file), so the Release API should be updated accordingly.

To be consistent with this change, the same restriction should apply to the evidence data accessed via the ReleaseController.

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

Closes #26019 (closed)