Add v3.28.6 to CHANGELOG.md.
Add v3.28.6 to CHANGELOG.md.

(cherry picked from commit c76034a9a22b1c38bc4b1dfb7394f95560e821b1)

emberjs/ember.js,sly7-7/ember.js,mixonic/ember.js,mixonic/ember.js,tildeio/ember.js,emberjs/ember.js,sly7-7/ember.js,tildeio/ember.js,tildeio/ember.js,emberjs/ember.js,mixonic/ember.js,sly7-7/ember.js