Add legacy platform names for old macos fleet (#1980)

Related:
https://github.com/bazelbuild/continuous-integration/issues/1708
diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index 27537ea..468f9aa 100755
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -521,6 +521,13 @@
         "queue": "macos",
         "python": "python3",
     },
+    "macos_legacy": {
+        "name": "macOS",
+        "emoji-name": ":darwin: macOS",
+        "publish_binary": [],
+        "queue": "macos_legacy",
+        "python": "python3",
+    },
     "macos_v2": {
         "name": "macOS",
         "emoji-name": ":darwin: macOS",
@@ -549,6 +556,13 @@
         "queue": "macos_arm64",
         "python": "python3",
     },
+    "macos_arm64_legacy": {
+        "name": "macOS arm64",
+        "emoji-name": ":darwin: macOS arm64",
+        "publish_binary": [],
+        "queue": "macos_arm64_legacy",
+        "python": "python3",
+    },
     "macos_arm64_v2": {
         "name": "macOS arm64",
         "emoji-name": ":darwin: macOS arm64",