Annotate type hint for STRUCT_TYPES listing.

Author: acolomb

canopen/objectdictionary/__init__.py

@@ -281,7 +281,7 @@ def add_member(self, variable: ODVariable) -> None:
 class ODVariable:
     """Simple variable."""
 
-    STRUCT_TYPES = {
+    STRUCT_TYPES: dict[int, struct.Struct] = {
         # Use struct module to pack/unpack data where possible and use the
         # custom IntegerN and UnsignedN classes for the special data types.
         BOOLEAN: struct.Struct("?"),