[mypy] Fix mypy warnings in api_server.py (#11941)

Signed-off-by: Fred Reiss <frreiss@us.ibm.com>

vllm/entrypoints/openai/api_server.py

@@ -14,7 +14,7 @@ from argparse import Namespace
 from contextlib import asynccontextmanager
 from functools import partial
 from http import HTTPStatus
-from typing import AsyncIterator, Optional, Set, Tuple
+from typing import AsyncIterator, Dict, Optional, Set, Tuple, Union
 
 import uvloop
 from fastapi import APIRouter, FastAPI, HTTPException, Request
@@ -420,6 +420,8 @@ async def create_embedding(request: EmbeddingRequest, raw_request: Request):
             "use the Pooling API (`/pooling`) instead.")
 
         res = await fallback_handler.create_pooling(request, raw_request)
+
+        generator: Union[ErrorResponse, EmbeddingResponse]
         if isinstance(res, PoolingResponse):
             generator = EmbeddingResponse(
                 id=res.id,
@@ -494,7 +496,7 @@ async def create_score_v1(request: ScoreRequest, raw_request: Request):
     return await create_score(request, raw_request)
 
 
-TASK_HANDLERS = {
+TASK_HANDLERS: Dict[str, Dict[str, tuple]] = {
     "generate": {
         "messages": (ChatCompletionRequest, create_chat_completion),
         "default": (CompletionRequest, create_completion),
@@ -652,7 +654,7 @@ def build_app(args: Namespace) -> FastAPI:
         module_path, object_name = middleware.rsplit(".", 1)
         imported = getattr(importlib.import_module(module_path), object_name)
         if inspect.isclass(imported):
-            app.add_middleware(imported)
+            app.add_middleware(imported)  # type: ignore[arg-type]
         elif inspect.iscoroutinefunction(imported):
             app.middleware("http")(imported)
         else: