infra: Update comment for macOS version used in CQ/CI

Bug: 433861937
Change-Id: I2e8ca940c59135cde988f397d0da1cff3977a674
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/19600
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@google.com>

infra/config/main.star

diff --git a/infra/config/main.star b/infra/config/main.star
index 3cb126e..ddfaaf3 100755
--- a/infra/config/main.star
+++ b/infra/config/main.star
@@ -120,6 +120,9 @@
     )
 
 ci_builder("linux", "Ubuntu-22.04")
+
+# macOS version for this builder should be synced with
+# https://source.corp.google.com/h/chromium/infra/infra_superproject/+/main:infra_internal/infra/config/subprojects/gn.star
 ci_builder("mac", "Mac-13", caches = [swarming.cache("macos_sdk")])
 ci_builder("win", "Windows-10", caches = [swarming.cache("windows_sdk")])
 
@@ -197,5 +200,8 @@
     )
 
 try_builder("linux", "Ubuntu-22.04")
+
+# macOS version for this builder should be synced with
+# https://source.corp.google.com/h/chromium/infra/infra_superproject/+/main:infra_internal/infra/config/subprojects/gn.star
 try_builder("mac", "Mac-13", caches = [swarming.cache("macos_sdk")])
 try_builder("win", "Windows-10", caches = [swarming.cache("windows_sdk")])