Fix migration to sync issuables with unknown states

What does this MR do?

Improve a migration from 12.4 to sync issuable with invalid states.

It is unusual to change migrations that already ran, but in this case we are doing it to prevent
people upgrading from old GitLab versions with a very specific case having problems.

For more information check: #35147 (closed)
More details in the discussion: #35147 (comment 237485644)

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• 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