chore: drop Python 3.9 (and syntax) (#6289)

* `strict=False` is the default, pyupgrade to min version 3.10 adds this
to be explicit w/ behavior

libs/checkpoint-postgres/langgraph/checkpoint/postgres/__init__.py

@@ -94,6 +94,7 @@ class PostgresSaver(BasePostgresSaver):
             for v, migration in zip(
                 range(version + 1, len(self.MIGRATIONS)),
                 self.MIGRATIONS[version + 1 :],
+                strict=False,
             ):
                 cur.execute(migration)
                 cur.execute(f"INSERT INTO checkpoint_migrations (v) VALUES ({v})")