add missing fixture for IssueTest#test_update_should_notify_previous_assignee

git-svn-id: http://svn.redmine.org/redmine/trunk@16894 e93f8b46-1217-0410-a6f0-8f06a7374b81

test/unit/issue_test.rb

@@ -26,6 +26,7 @@ class IssueTest < ActiveSupport::TestCase
            :issue_statuses, :issue_categories, :issue_relations, :workflows,
            :enumerations,
            :issues, :journals, :journal_details,
+           :watchers,
            :custom_fields, :custom_fields_projects, :custom_fields_trackers, :custom_values,
            :time_entries