chore: Pin m6i/5.10 AMI to last known good one

We're observing performance instability on m6i/5.10 which is causing A/B
performance test failures. To suppress false positives, pin AMI to the
last known good one only for m6i/5.10.

Signed-off-by: Takahiro Itazuri <[email protected]>

Author: zulinx86

.buildkite/pipeline_perf.py

@@ -119,7 +119,10 @@
 # }
 # will pin steps running on instances "m6i.metal" with kernel version tagged "linux_6.1"
 # to a new kernel version tagged "linux_6.1-pinned"
-pins = {}
+pins = {
+    # TODO: Unpin when performance instability on m6i/5.10 has gone.
+    "linux_5.10-pinned": {"instance": "m6i.metal", "kv": "linux_5.10"},
+}
 
 
 def apply_pins(steps):