issuable_actions.rb

For issuable models we keep two timestamps:
updated_at which is updated whenever any model attribute is changed,
last_edited_at which is changed when only title or description is
changed.

In UI bellow description we display who and when updated the item. But
last_edited_by (used for 'who') is mistakenly combined with updated_at
(when), last_edited_at should be used instead.

Closes #41247