exclude bair.berkeley.edu temporarily (#2702)

markdown-link-check.config.json

         {
             "pattern": "^https://developer.nvidia.com/compute/machine-learning/cudnn/secure",
             "comment": "Requires login"
+        },
+        {
+            "pattern": "^https?://bair.berkeley.edu",
+            "comment": "Temporary berkeley outage"
         }
     ]
 }