Use build_stubbed to remove unnecessary DB calls in packages validations

What does this MR do?

Removes unnecessary db queries when running packges specs by using /build and build_stubbed when testing validations.

Queries saved: 7795

Before:

[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:18.563 of 00:33.802 (54.92%)
Total events: 15783

After:

[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:09.278 of 00:18.168 (51.07%)
Total events: 7988

Screenshots

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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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