Fix zindex of popup on mobile (#3890)

Fixes #3506. Credit to @Teranode

modules/system/assets/ui/less/dropdown.less

@@ -256,7 +256,7 @@ body.dropdown-open {
             right: 0!important;
             bottom: 0!important;
             left: 0!important;
-            z-index: @zindex-modal-background;
+            z-index: @zindex-dropdown;
 
             .dropdown-container {
                 padding: 10px;
@@ -297,4 +297,4 @@ body.dropdown-open {
             }
         }
     }
-}
+}

modules/system/controllers/updates/_list_manage_toolbar.htm

@@ -17,7 +17,7 @@
             <?= e(trans('system::lang.plugins.select_label')) ?>
         </button>
 
-        <ul class="dropdown-menu" data-dropdown-title="<?= e(trans('rainlab.user::lang.users.bulk_actions')) ?>">
+        <ul class="dropdown-menu" data-dropdown-title="<?= e(trans('system::lang.plugins.bulk_actions_label')) ?>">
             <li>
                 <a href="javascript:;" class="oc-icon-pause"
                    data-request="onBulkAction"

modules/system/lang/en/lang.php

@@ -111,6 +111,7 @@ return [
         'plugin_label'  => 'Plugin',
         'unknown_plugin' => 'Plugin has been removed from the file system.',
         'select_label' => 'Select Action...',
+        'bulk_actions_label' => 'Bulk actions',
         'check_yes' => 'Yes',
         'check_no' => 'No',
         'unfrozen' => 'Updates Enabled',