[CI] Update merge condition to skip L3 merges during weekly test and update doc (#3197)

Signed-off-by: zhumingjue <zhumingjue@huawei.com>

docs/contributing/ci/test_guide.md

@@ -91,10 +91,16 @@ Our test scripts use the pytest framework. First, please use `git clone https://
     cd tests
 
     # Stability: Qwen3-Omni
-    pytest -s -v dfx/stability/scripts/test_stability_qwen3_omni.py
+    pytest -s -v dfx/stability/scripts/test_stability_qwen3_omni.py -m slow
 
     # Stability: Wan2.2 (v1/videos diffusion benchmark loop)
-    pytest -s -v dfx/stability/scripts/test_stability_wan22.py
+    pytest -s -v dfx/stability/scripts/test_stability_wan22.py -m slow
+
+    # Reliability: Qwen3-Omni
+    pytest -s -v dfx/reliability/test_reliability_qwen3_omni.py -m slow
+
+    # Reliability: Wan2.2
+    pytest -s -v dfx/reliability/test_reliability_wan22.py -m slow
 
     ```