fix: isolate GROQ_API_KEY in test_missing_stt_key test

The test was failing because GROQ_API_KEY leaked from the environment.
Now both VOICE_TOOLS_OPENAI_KEY and GROQ_API_KEY are removed to
properly test the "no STT key" scenario.

tests/tools/test_voice_mode.py

@@ -86,6 +86,7 @@ class TestCheckVoiceRequirements:
     def test_missing_stt_key(self, monkeypatch):
         monkeypatch.setattr("tools.voice_mode._HAS_AUDIO", True)
         monkeypatch.delenv("VOICE_TOOLS_OPENAI_KEY", raising=False)
+        monkeypatch.delenv("GROQ_API_KEY", raising=False)
 
         from tools.voice_mode import check_voice_requirements