Merge branch 'issuable-dropdowns-changelog' into 'master'

Added changelog item for issuable form dropdowns

## What does this MR do?

Adds CHANGELOG item about the new dropdowns in the issuable form

See merge request !5266

CHANGELOG

@@ -169,6 +169,9 @@ v 8.10.0
   - Fix check for New Branch button on Issue page. !4630 (winniehell)
   - Fix GFM autocomplete not working on wiki pages
   - Fixed enter key not triggering click on first row when searching in a dropdown
+  - Updated dropdowns in issuable form to use new GitLab dropdown style
+  - Make images fit to the size of the viewport !4810
+  - Fix check for New Branch button on Issue page !4630 (winniehell)
   - Fix MR-auto-close text added to description. !4836
   - Support U2F devices in Firefox. !5177
   - Fix issue, preventing users w/o push access to sort tags. !5105 (redetection)