Add v3.21.0-beta.2 to CHANGELOG [ci skip]
Add v3.21.0-beta.2 to CHANGELOG
[ci skip]

(cherry picked from commit 1be10910593f135cdefb2b8ecfbb932dba061c1e)

givanse/ember.js,givanse/ember.js,givanse/ember.js,emberjs/ember.js,tildeio/ember.js,sly7-7/ember.js,sandstrom/ember.js,sandstrom/ember.js,mfeckie/ember.js,mixonic/ember.js,mixonic/ember.js,knownasilya/ember.js,mfeckie/ember.js,givanse/ember.js,stefanpenner/ember.js,mfeckie/ember.js,mixonic/ember.js,sandstrom/ember.js,emberjs/ember.js,elwayman02/ember.js,tildeio/ember.js,elwayman02/ember.js,sly7-7/ember.js,stefanpenner/ember.js,mfeckie/ember.js,knownasilya/ember.js,elwayman02/ember.js,emberjs/ember.js,sly7-7/ember.js,stefanpenner/ember.js,knownasilya/ember.js,elwayman02/ember.js,tildeio/ember.js