feat(tests): Set default environment variables for CI/unit tests

Set default environment variables for Discord and Lavalink in `conftest.py`. This ensures the configuration bootstrap has the necessary secrets during CI and local unit testing, preventing failures due to missing environment variables.

Author: timhauke

tests/conftest.py

@@ -1,9 +1,16 @@
 """Pytest configuration helpers."""
 
+import os
 import sys
 from pathlib import Path
 
 ROOT = Path(__file__).resolve().parents[1]
 
 if str(ROOT) not in sys.path:
     sys.path.insert(0, str(ROOT))
+
+# Ensure config bootstrap has the secrets it needs during CI/unit tests.
+os.environ.setdefault("DISCORD_TOKEN", "TEST_TOKEN")
+os.environ.setdefault("LAVALINK_HOST", "localhost")
+os.environ.setdefault("LAVALINK_PORT", "2333")
+os.environ.setdefault("LAVALINK_PASSWORD", "testing-token")