stdlib: add argument default values (#9501)

stdlib/distutils/spawn.pyi

@@ -1,2 +1,2 @@
 def spawn(cmd: list[str], search_path: bool = ..., verbose: bool = ..., dry_run: bool = ...) -> None: ...
-def find_executable(executable: str, path: str | None = ...) -> str | None: ...
+def find_executable(executable: str, path: str | None = None) -> str | None: ...