message: Add entry in CHANGELOG.
diff: ### Bugfixes
  -* Lorem ipsum.
  +* Fix for incorrect, redundant string index tree traversal for case insensitive searches
  + for strings with some characters being identical in upper and lower case (e.g. numbers).
  + PR [#2578](https://github.com/realm/realm-core/pull/2578),
  + Cocoa issue [#4895](https://github.com/realm/realm-cocoa/issues/4895)
  ### Breaking changes
  