saml: deal with set attributes (#42646)

src/authentic2/saml/models.py

@@ -335,7 +335,7 @@ class SAMLAttribute(models.Model):
         name = self.name
         friendly_name = self.friendly_name or None
         values = ctx.get(self.attribute_name)
-        if not isinstance(values, list):
+        if not isinstance(values, (list, tuple, set)):
             values = [values]
         for value in values:
             yield (name, name_format, friendly_name, value)