Merge branch 'ebaque-remove-milestone-from-board-import-export' into 'master'

Remove milestone attribute from board import export yaml [RUN AS-IF-FOSS]

See merge request gitlab-org/gitlab!71884

lib/gitlab/import_export/group/import_export.yml

@@ -10,7 +10,6 @@ tree:
     - labels:
       - :priorities
     - boards:
-      - :milestone
       - lists:
         - label:
           - :priorities