Fix baseinvocation use of __attribute__ to work with py3.9 (#4413)

## What type of PR is this? (check all applicable)

- [X] Bug Fix

## Have you discussed this change with the InvokeAI team?
- [X] Yes
      
## Have you updated all relevant documentation?
- [X] Yes

## Description

There is a call in `baseinvocation.invocation_output()` to
`cls.__annotations__`. However, in Python 3.9 not all objects have this
attribute. I have worked around the limitation in the way described in
https://docs.python.org/3/howto/annotations.html , which supposedly will
produce same results in 3.9, 3.10 and 3.11.


## Related Tickets & Documents

See
https://discord.com/channels/1020123559063990373/1146897072394608660/1146939182300799017
for first bug report.

invokeai/app/invocations/baseinvocation.py

@@ -580,8 +580,9 @@ def invocation(
             config=cls.__config__,
         )
         cls.__fields__.update({"type": invocation_type_field})
-        cls.__annotations__.update({"type": invocation_type_annotation})
-
+        # to support 3.9, 3.10 and 3.11, as described in https://docs.python.org/3/howto/annotations.html
+        if annotations := cls.__dict__.get("__annotations__", None):
+            annotations.update({"type": invocation_type_annotation})
         return cls
 
     return wrapper
@@ -615,7 +616,10 @@ def invocation_output(
             config=cls.__config__,
         )
         cls.__fields__.update({"type": output_type_field})
-        cls.__annotations__.update({"type": output_type_annotation})
+
+        # to support 3.9, 3.10 and 3.11, as described in https://docs.python.org/3/howto/annotations.html
+        if annotations := cls.__dict__.get("__annotations__", None):
+            annotations.update({"type": output_type_annotation})
 
         return cls