Use checkbox list instead of select for admin users.

This way it is harder to unselect the admin users, to avoid
accidentally unselected them if ctrl isn't being held down.

templates/ContentGenerator/CourseAdmin/add_course_form.html.ep

@@ -41,12 +41,18 @@
 			<%= maketext(
 				'Select admin course users to add to the new course (as the stated permission) below.') =%>
 		</div>
-		<div class="col-lg-4 col-md-5 col-sm-6">
-			<%= select_field 'add-admin-users' => [ map {
-				my $val   = $db->getPermissionLevel($_)->permission;
-				my $level = maketext((grep { $ce->{userRoles}{$_} eq $val } keys %{ $ce->{userRoles} })[0]);
-				[ "$_ ($level)" => $_, $val == 20 ? (selected => undef) : () ] } $db->listUsers ],
-				size => 5, multiple => undef, class =>'form-select mb-1' =%>
+		<div class="col-lg-4 col-md-5 col-sm-6 overflow-scroll border rounded px-2" style="height: 100px;">
+			% for my $user ($db->listUsers) {
+				% my $val   = $db->getPermissionLevel($user)->permission;
+				% my $level = maketext((grep { $ce->{userRoles}{$_} eq $val } keys %{ $ce->{userRoles} })[0]);
+				<div class="form-check">
+					<label class="form-check-label">
+						<%= check_box 'add-admin-users' => $user, class => 'form-check-input',
+							$val == 20 ? (checked => undef) : () =%>
+						<%= "$user ($level)" %>
+					</label>
+				</div>
+			% }
 		</div>
 	</div>
 	<div class="mb-2">