Add work_item_related_link_restrictions to deletion exceptions

Related to gitlab-org/quality/engineering-productivity/master-broken-incidents#3905 (closed)

What does this MR do and why?

Add work_item_related_link_restrictions to deletion exceptions. We have to keep the records in this table because they are needed for tests. See gitlab-org/quality/engineering-productivity/master-broken-incidents#3905 (comment 1608742052)

MR acceptance checklist

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

• I have evaluated the MR acceptance checklist for this MR.

Related to #424880 (closed)