Remove the incorrect Optional from FormatChecker's formats annotation.

See https://docs.python.org/3/library/typing.html#typing.Optional.

This is meant to be used only if None is a specifically allowed value, where
here it is not, it's an internal sentinel, not part of its public API, which
only allows iterables.

jsonschema/_format.py

@@ -44,7 +44,7 @@ class FormatChecker:
         tuple[_FormatCheckCallable, _RaisesType],
     ] = {}
 
-    def __init__(self, formats: typing.Iterable[str] | None = None):
+    def __init__(self, formats: typing.Iterable[str] = None):
         if formats is None:
             formats = self.checkers.keys()
         self.checkers = {k: self.checkers[k] for k in formats}