fix(dependency): add back typing-extensions for 3.9 (#1358)

Missing typing-extensions breaks "from libcst.codemod import CodemodContext"

Author: Lee-W

pyproject.toml

@@ -21,6 +21,7 @@ requires-python = ">=3.9"
 dependencies = [
     "pyyaml>=5.2; python_version < '3.13'",
     "pyyaml-ft>=8.0.0; python_version >= '3.13'",
+    "typing-extensions; python_version < '3.10'",
 ]
 
 [project.urls]