pwa: use icon file basename during import (#53720)

Django 2.2.21 introduced the validation of FieldFile.save() name
argument, which cannot contain a path separator anymore. To use the
received FileField value as a base filename, we must apply
os.path.basename() on it first.

ref. https://docs.djangoproject.com/en/3.2/releases/2.2.21/

combo/apps/pwa/models.py

@@ -18,6 +18,7 @@
 
 import base64
 import json
+import os
 
 from django.conf import settings
 from django.core import serializers
@@ -188,7 +189,7 @@ class PwaNavigationEntry(models.Model):
             decoded_icon = base64.decodebytes(force_bytes(json_entry['icon:base64']))
             if not default_storage.exists(entry.object.icon.name) or entry.object.icon.read() != decoded_icon:
                 # save new file
-                entry.object.icon.save(entry.object.icon.name, ContentFile(decoded_icon))
+                entry.object.icon.save(os.path.basename(entry.object.icon.name), ContentFile(decoded_icon))
 
 
 class PushSubscription(models.Model):