fix: datasets django4.2 facet variable (#1617)

Author: lukasvinclav

src/unfold/templatetags/unfold_list.py

@@ -11,7 +11,6 @@
 from django.contrib.admin.templatetags.base import InclusionAdminNode
 from django.contrib.admin.utils import label_for_field, lookup_field
 from django.contrib.admin.views.main import (
-    IS_FACETS_VAR,
     IS_POPUP_VAR,
     ORDER_VAR,
     PAGE_VAR,
@@ -40,6 +39,12 @@
 from unfold.views import DatasetChangeList
 from unfold.widgets import UnfoldBooleanWidget
 
+try:
+    from django.contrib.admin.views.main import IS_FACETS_VAR
+except ImportError:
+    # TODO: remove once django 4.x is not supported
+    IS_FACETS_VAR = None
+
 register = Library()
 
 LINK_CLASSES = [