[mypy] Enable type checking for test directory (#5017)

vllm/model_executor/models/gemma.py

@@ -15,7 +15,7 @@
 # limitations under the License.
 """Inference-only Gemma model compatible with HuggingFace weights."""
 from functools import lru_cache
-from typing import Iterable, List, Optional, Tuple
+from typing import Iterable, List, Optional, Set, Tuple
 
 import torch
 from torch import nn
@@ -363,7 +363,7 @@ class GemmaForCausalLM(nn.Module):
             ("gate_up_proj", "up_proj", 1),
         ]
         params_dict = dict(self.named_parameters())
-        loaded_params = set()
+        loaded_params: Set[str] = set()
         for name, loaded_weight in weights:
             for (param_name, shard_name, shard_id) in stacked_params_mapping:
                 if shard_name not in name: