Prevent uploading files with unmatching accept attribute

formset/widgets.py

@@ -12,7 +12,8 @@
 from django.db.models.query_utils import Q
 from django.forms.widgets import FILE_INPUT_CONTRADICTION
 from django.forms.models import ModelChoiceIterator, ModelChoiceIteratorValue
-from django.forms.widgets import DateTimeBaseInput, FileInput, Select, SelectMultiple, TextInput, Widget
+from django.forms.widgets import (DateTimeBaseInput, FileInput, FILE_INPUT_CONTRADICTION, Select, SelectMultiple,
+    TextInput, Widget)
 from django.template.loader import get_template
 from django.utils.encoding import uri_to_iri
 from django.utils.functional import cached_property