Added All word to warning statement for plural abtests

Author: joelwilliam2005

wagtail_ab_testing/templates/wagtail_ab_testing/confirm_delete_ab_tests.html

@@ -10,7 +10,7 @@
             {% blocktrans count counter=ab_tests_count %}
                 1 A/B test associated with this page will be permanently deleted.
             {% plural %}
-                {{ counter }} A/B tests associated with this page will be permanently deleted.
+                All {{ counter }} A/B tests associated with this page will be permanently deleted.
             {% endblocktrans %}
         </p>
             <table class="listing">