Set buck2 version on MacOS

Author: huydhn

.ci/scripts/setup-macos.sh

@@ -28,15 +28,8 @@ install_buck() {
   fi
 
   pushd .ci/docker
-
-  # TODO(huydo): This is a one-off copy of buck2 2024-05-15 to unblock Jon and
-  # re-enable ShipIt. It’s not ideal that upgrading buck2 will require a manual
-  # update the cached binary on S3 bucket too. Let me figure out if there is a
-  # way to correctly implement the previous setup of installing a new version of
-  # buck2 only when it’s needed. AFAIK, the complicated part was that buck2
-  # --version doesn't say anything w.r.t its release version, i.e. 2024-05-15.
-  # See D53878006 for more details.
-  BUCK2=buck2-aarch64-apple-darwin.zst
+  BUCK2_VERSION=2024-05-15
+  BUCK2=buck2-aarch64-apple-darwin-${BUCK2_VERSION}.zst
   curl -s "https://ossci-macos.s3.amazonaws.com/${BUCK2}" -o "${BUCK2}"
 
   zstd -d "${BUCK2}" -o buck2