docs: improve CI and testing documentation (#21202)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sgl-kernel/tests/test_gguf.py

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 import random
+import sys
 from pathlib import Path
 
 import numpy as np
@@ -163,4 +164,4 @@ def test_mmq(
 
 
 if __name__ == "__main__":
-    pytest.main([__file__])
+    sys.exit(pytest.main([__file__]))