Fix install_import_hook(..., None)

jaxtyping/_import_hook.py

@@ -109,7 +109,7 @@ def __init__(self, typechecker):
 
         elif typechecker is None:
             # If it is None, ignore it silently (use dummy decorator)
-            self.hash = 0
+            self.hash = "0"
             Typechecker.lookup[self.hash] = lambda x, *_, **__: x
         else:
             # Passed typechecker is invalid