Update contributions calendar UNION query

Explicitly list columns to be selected, to avoid PG::UndefinedColumn
error when column on `Event` is ignored.

See
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/69337#note_667082434.

lib/gitlab/contributions_calendar.rb

@@ -33,6 +33,7 @@ module Gitlab
         .having(action: :commented)
 
       events = Event
+        .select(:project_id, :target_type, :action, :date, :total_amount)
         .from_union([repo_events, issue_events, mr_events, note_events])
         .map(&:attributes)