[1.4.x] Fixed #20906 -- Fixed a dependence on set-ordering in tests

Backport of 1ae64e9 from master

tests/regressiontests/admin_filters/tests.py

@@ -82,11 +82,11 @@ class DepartmentListFilterLookupWithNonStringValue(SimpleListFilter):
     parameter_name = 'department'
 
     def lookups(self, request, model_admin):
-        return set([
+        return sorted(set([
             (employee.department.id,  # Intentionally not a string (Refs #19318)
              employee.department.code)
             for employee in model_admin.queryset(request).all()
-        ])
+        ]))
 
     def queryset(self, request, queryset):
         if self.value():
@@ -681,10 +681,9 @@ def test_lookup_with_non_string_value(self):
         filterspec = changelist.get_filters(request)[0][-1]
         self.assertEqual(force_unicode(filterspec.title), u'department')
         choices = list(filterspec.choices(changelist))
-
-        self.assertEqual(choices[2]['display'], u'DEV')
-        self.assertEqual(choices[2]['selected'], True)
-        self.assertEqual(choices[2]['query_string'], '?department=%s' % self.john.pk)
+        self.assertEqual(choices[1]['display'], 'DEV')
+        self.assertEqual(choices[1]['selected'], True)
+        self.assertEqual(choices[1]['query_string'], '?department=%s' % self.john.pk)
 
     def test_fk_with_to_field(self):
         """