Fixed boards filters

app/controllers/projects/boards_controller.rb

 class Projects::BoardsController < Projects::ApplicationController
+  include IssuableCollections
+  
   respond_to :html
   before_action :authorize_read_board!, only: [:show]

app/views/shared/issuable/_filter.html.haml

-- finder = controller.controller_name == 'issues' ? issues_finder : merge_requests_finder
+- finder = controller.controller_name == 'issues' || controller.controller_name == 'boards' ? issues_finder : merge_requests_finder
 .issues-filters
   .issues-details-filters.row-content-block.second-block
     = form_tag page_filter_path(without: [:assignee_id, :author_id, :milestone_title, :label_name, :issue_search]), method: :get, class: 'filter-form js-filter-form' do