Add __all__ part 2 (#13719)

---------

Co-authored-by: Avasam <samuel.06@hotmail.com>

stubs/httplib2/@tests/stubtest_allowlist.txt

@@ -1,5 +1,2 @@
-# TODO: missing from stub
-httplib2.__all__
-
 # __getattr__() replaced with actual field in stub
 httplib2.Response.dict

stubs/httplib2/httplib2/__init__.pyi

@@ -186,3 +186,17 @@ class Response(dict[str, Any]):
     def __init__(self, info) -> None: ...
     @property
     def dict(self) -> Self: ...
+
+__all__ = [
+    "debuglevel",
+    "FailedToDecompressContent",
+    "Http",
+    "HttpLib2Error",
+    "ProxyInfo",
+    "RedirectLimit",
+    "RedirectMissingLocation",
+    "Response",
+    "RETRIES",
+    "UnimplementedDigestAuthOptionError",
+    "UnimplementedHmacDigestAuthOptionError",
+]