providers/saml: fix error when PropertyMapping return value isn't string

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

authentik/providers/saml/processors/assertion.py

@@ -157,7 +157,7 @@ class AssertionProcessor:
                     provider=self.provider,
                 )
                 if value is not None:
-                    name_id.text = value
+                    name_id.text = str(value)
                 return name_id
             except PropertyMappingExpressionException as exc:
                 Event.new(