stdlib: fix many attributes which are read-only at runtime but read-write in the stub (#7395)

stdlib/shlex.pyi

@@ -29,7 +29,11 @@ class shlex(Iterable[str]):
     lineno: int
     token: str
     eof: str
-    punctuation_chars: str
+    if sys.version_info >= (3, 7):
+        @property
+        def punctuation_chars(self) -> str: ...
+    else:
+        punctuation_chars: str
     def __init__(
         self,
         instream: str | TextIO | None = ...,