chore: Pin 5.10 kernel AMIs

We are running into io_uring test failures after 5.10 kernel update on
2024-04-19. The issue is under investigation, but it prevents us from
merging PRs and it makes multiple pipelines fail. Until solving the
issue, pin 5.10 kernel AMIs to older ones and set them default.

Signed-off-by: Takahiro Itazuri <itazur@amazon.com>

.buildkite/common.py

@@ -22,7 +22,8 @@
 
 DEFAULT_PLATFORMS = [
     ("al2", "linux_4.14"),
-    ("al2", "linux_5.10"),
+    # TODO: Unpin 5.10 kernel AMI once io_uring issues is solved.
+    ("al2", "linux_5.10-pinned"),
     ("al2023", "linux_6.1"),
 ]