stdlib: add argument default values (#9501)

stdlib/ensurepip/__init__.pyi

@@ -3,10 +3,10 @@ __all__ = ["version", "bootstrap"]
 def version() -> str: ...
 def bootstrap(
     *,
-    root: str | None = ...,
-    upgrade: bool = ...,
-    user: bool = ...,
-    altinstall: bool = ...,
-    default_pip: bool = ...,
-    verbosity: int = ...,
+    root: str | None = None,
+    upgrade: bool = False,
+    user: bool = False,
+    altinstall: bool = False,
+    default_pip: bool = False,
+    verbosity: int = 0,
 ) -> None: ...