add labels to course visibility options

fixes CNVS-31302

Test Plan:
- In Safari with VoiceOver enabled, open the Settings page of a
  course
- Move VO focus to the Visibility combo box
- Note that the current value and "pop up button" is read, and
  the label is also read

Change-Id: Idc45f05e01297f4378c366f5675f76625cfde46f
Reviewed-on: https://gerrit.instructure.com/89401
Tested-by: Jenkins
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
QA-Review: Deepeeca Soundarrajan <dsoundarrajan@instructure.com>
Product-Review: Steven Burnett <sburnett@instructure.com>

app/views/courses/settings.html.erb

@@ -286,7 +286,7 @@
         <td colspan="3" id="course_visibility">
           <% if can_manage %>
             <span>
-              <%= f.select :course_visibility, @context.course_visibility_options.map{ |id, attrs| [attrs[:setting], id] } %>
+              <%= f.select :course_visibility, @context.course_visibility_options.map{ |id, attrs| [attrs[:setting], id] }, {},  {"aria-label" => t("Course Visibility Options")} %>
               <%= visibility_help_link %>
             </span>
             <div class="panel-border">
@@ -295,7 +295,7 @@
               <% @context.customize_course_visibility_list.map do |setting, options| %>
                 <div id="customize_course_visibility">
                   <%= f.label :syllabus_visibility_option, options[:setting] %>
-                  <%= f.select :syllabus_visibility_option, @context.course_visibility_options.map{ |id, attrs| [attrs[:setting], "#{id}"] }, {}, :id => options[:setting] %>
+                  <%= f.select :syllabus_visibility_option, @context.course_visibility_options.map{ |id, attrs| [attrs[:setting], "#{id}"] }, {}, {:id => options[:setting], "aria-label" => t("Syllabus Visibility Options")} %>
                 </div>
               <% end %>
             </div>