feat(buildkite): add Granite Rapids instances to test defaults

Add Granite Rapids instances (m8i.metal-{48,96}xl) to the list of
default tested instances for buildkite.

Signed-off-by: James Curtis <jxcurtis@amazon.co.uk>

Author: JamesC1305

.buildkite/common.py

@@ -20,6 +20,8 @@
     "m6i.metal",      # Intel Ice Lake
     "m7i.metal-24xl", # Intel Sapphire Rapids
     "m7i.metal-48xl", # Intel Sapphire Rapids
+    "m8i.metal-48xl", # Intel Granite Rapids
+    "m8i.metal-96xl", # Intel Granite Rapids
     "m6a.metal",      # AMD Milan
     "m7a.metal-48xl", # AMD Genoa
     "m6g.metal",      # Graviton2