[Backend Tester] Mark adaptive avgpool2d as an unsupported portable op

ghstack-source-id: b334830
ghstack-comment-id: 3186214612
Pull-Request: #13398

Author: GregoryComer

backends/test/suite/runner.py

@@ -15,6 +15,7 @@
 # Set of unsupported ops that should cause tests to be skipped
 UNSUPPORTED_PORTABLE_OPS = {
     "aten::_embedding_bag",
+    "aten::_adaptive_avg_pool2d",
     "aten::median",
     "aten::median.dim",
     "aten::round.decimals",