ci: Disable A/B tests failing on m6i.metal 5.10

An AMI update in CI introduced high volatility on m6i.metal 5.10
affecting a large number of performance. This commit disables failing on
this configuration to avoid spurious failures until the AMI is updated
and the volatility has subsided.

Signed-off-by: Jonathan Woollett-Light <jcawl@amazon.co.uk>

tools/ab_test.py

@@ -49,6 +49,11 @@
         "host_kernel": "linux-5.10",
         "vcpus": "1",
     },
+    # High volatility due to AMI.
+    {
+        "instance": "m6i.metal",
+        "host_kernel": "linux-5.10",
+    },
 ]