Add various missing generic arguments (#7702)

Co-authored-by: Akuli <akuviljanen17@gmail.com>

stubs/Pillow/PIL/PdfParser.pyi

@@ -47,10 +47,10 @@ class PdfName:
 class PdfArray(list[Any]):
     def __bytes__(self): ...
 
-class PdfDict(collections.UserDict):
+class PdfDict(collections.UserDict[bytes, Any]):
     def __setattr__(self, key, value) -> None: ...
     def __getattr__(self, key): ...
-    def __bytes__(self): ...
+    def __bytes__(self) -> bytes: ...
 
 class PdfBinary:
     data: Any