Add cores as a dimension.

This is required to select highmem bot for clang tidy builds.

Bug: https://github.com/flutter/flutter/issues/98529
Change-Id: I135a7339811b8907045ebfb444bea10ec2b9201f
diff --git a/config/lib/ci_yaml/ci_yaml.star b/config/lib/ci_yaml/ci_yaml.star
index 38aefdc..e181189 100644
--- a/config/lib/ci_yaml/ci_yaml.star
+++ b/config/lib/ci_yaml/ci_yaml.star
@@ -327,7 +327,7 @@
         }
         if platform in dimensions:
             target_args["dimensions"] = dimensions[platform]
-        dimension_key_list = ("device_type", "device_os", "mac_model")
+        dimension_key_list = ("device_type", "device_os", "mac_model", "cores")
         platform_properties = _platform_properties(ci_yaml)[platform]
         for dimension_key in dimension_key_list:
             if dimension_key in platform_properties: