[CI] Bump mypy version to 1.19.1 (#36104)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/sampling_params.py

@@ -533,6 +533,7 @@ class SamplingParams(
             if eos_ids:
                 self._all_stop_token_ids.update(eos_ids)
                 if not self.ignore_eos:
+                    assert self.stop_token_ids is not None
                     eos_ids.update(self.stop_token_ids)
                     self.stop_token_ids = list(eos_ids)