ruff: Enable B008 function-call-in-default-argument.

https://docs.astral.sh/ruff/rules/function-call-in-default-argument/

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/lib/types.py

@@ -69,7 +69,7 @@ class LinkifierDict(TypedDict):
     id: int
 
 
-class UnspecifiedValue:
+class Unset:
     """In most API endpoints, we use a default value of `None"` to encode
     parameters that the client did not pass, which is nicely Pythonic.
 
@@ -84,6 +84,9 @@ class UnspecifiedValue:
     """
 
 
+UNSET = Unset()
+
+
 class EditHistoryEvent(TypedDict, total=False):
     """
     Database format for edit history events.