Fix test to handle different script tag format in Django 3.1

wagtail/admin/tests/tests.py

@@ -2,6 +2,7 @@
 
 import json
 
+from django import VERSION as DJANGO_VERSION
 from django.contrib.auth import get_user_model
 from django.contrib.auth.models import Group, Permission
 from django.core import mail
@@ -32,10 +33,19 @@ class TestHome(TestCase, WagtailTestUtils):
         response = self.client.get(reverse('wagtailadmin_home'))
         self.assertEqual(response.status_code, 200)
         # check that media attached to menu items is correctly pulled in
-        self.assertContains(
-            response,
-            '<script type="text/javascript" src="/static/testapp/js/kittens.js"></script>'
-        )
+        if DJANGO_VERSION >= (3, 1):
+            self.assertContains(
+                response,
+                '<script src="/static/testapp/js/kittens.js"></script>',
+                html=True
+            )
+        else:
+            self.assertContains(
+                response,
+                '<script type="text/javascript" src="/static/testapp/js/kittens.js"></script>',
+                html=True
+            )
+
         # check that custom menu items (including classname / attrs parameters) are pulled in
         self.assertContains(
             response,