[ci] add block for apple silicon test (#273)

the test does not run much, but often needs to wait for a long time

---------

Signed-off-by: Lonnie Liu <[email protected]>

Author: aslonnie

.buildkite/macos.rayci.yaml

@@ -1,16 +1,24 @@
 group: macos
 sort_key: "~macos"
 steps:
+  - block: "Run Apple Silicon MacOS Tests"
+    key: "macos-apple-silicon-block"
+    depends_on: ~
+
   - name: ":macos: apple silicon macos example"
     job_env: MACOS
     instance_type: macos-arm64
+    depends_on: "macos-apple-silicon-block"
     commands: 
       - echo "Hello, MacOS arm64!"
 
   - block: "Run Intel MacOS Tests"
+    key: "macos-intel-block"
+    depends_on: ~
 
   - name: ":macos: intel silicon macos example"
     job_env: MACOS
     instance_type: macos
+    depends_on: "macos-intel-block"
     commands: 
       - echo "Hello, MacOS!"