Migrate stardoc BazelCI to macos_arm64 (#312)

Fixes https://buildkite.com/bazel/bazel-at-head-plus-downstream/builds/5546/list?jid=019ecd05-779d-4897-a07e-ea1c23d102c8&tab=output

.bazelci/presubmit.yml

diff --git a/.bazelci/presubmit.yml b/.bazelci/presubmit.yml
index 53d90cf..01e301d 100644
--- a/.bazelci/presubmit.yml
+++ b/.bazelci/presubmit.yml
@@ -2,7 +2,7 @@
 matrix:
   platform:
     - ubuntu2004
-    - macos
+    - macos_arm64
 
 .noenable_bzlmod_flags: &noenable_bzlmod_flags
   ? "--noenable_bzlmod"