message: Prepare version 6.0.0-alpha.6
diff: -# NEXT RELEASE
  -
  -### Enhancements
  -* None.
  +# 6.0.0-alpha.6 Release notes
  ### Fixed
  -* <How to hit and notice issue? what was the impact?> ([#????](https://github.com/realm/realm-core/issues/????), since v?.?.?)
  -* None.
  -
  -### Breaking changes
  * None.
  -----------
  ### Internals
  -* None.
  +* Column keys cannot be used across tables. If a key is obtained from one table, it can only be
  + used in relation to that table.
  Besides the changes above, this release includes changes introduced by v5.16.0 and up
  until v5.17.0
  