Use only 4 local test jobs on macOS testing machines, as they are slower.
diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index 45548db..78add78 100755
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -1613,7 +1613,9 @@
         return "75"
     elif platform == "windows":
         return "8"
-    elif platform == "macos":
+    elif platform.startswith("macos") and THIS_IS_TESTING:
+        return "4"
+    elif platform.startswith("macos"):
         return "8"
     return "12"