[CI] Fix flaky tool_use chat completion tests with deterministic seed (#37027)

Signed-off-by: sfeng33 <4florafeng@gmail.com>

tests/tool_use/utils.py

@@ -42,6 +42,8 @@ def ensure_system_prompt(
 
 # universal args for all models go here. also good if you need to test locally
 # and change type or KV cache quantization or something.
+SEED = 42
+
 ARGS: list[str] = [
     "--enable-auto-tool-choice",
     "--max-model-len",