Revert exclude_none=True, exclude_unset=True, exclude_defaults=True…

… in error serialization.

`exclude_unset=True` and `exclude_defaults=True` do not do what we want because we define a lot of fields like `errorType: Literal["RunNotFoundError"] = "RunNotFoundError"`, and we definitely do want those to get serialized. The bug that was fixed in commit b5b28b6 was somehow covering up this problem, I think.

I'm ambivalent about `exclude_none=True` here, but I don't see a pressing reason for this upgrade to change it from what it was before, so let's delete that too.

robot-server/robot_server/errors/error_responses.py

@@ -25,12 +25,7 @@ class BaseErrorBody(BaseResponseBody):
 
     def as_error(self, status_code: int) -> ApiError:
         """Serialize the response as an API error to raise in a handler."""
-        return ApiError(
-            status_code=status_code,
-            content=self.model_dump(
-                exclude_none=True, exclude_unset=True, exclude_defaults=True
-            ),
-        )
+        return ApiError(status_code=status_code, content=self.model_dump())
 
 
 class ErrorSource(BaseModel):