DOC: clearify comment as to why only cygwin needs this config

Author: tacaswell

.github/zizmor.yml

@@ -12,8 +12,8 @@ rules:
   cache-poisoning:
     ignore:
       # cygwin.yml is a test-only workflow; no artifacts are published.
-      # The three caches (pip, ccache, matplotlib data) are purely for build
-      # acceleration and present no poisoning risk for released artifacts.
+      # This is triggering a low-confidence flag that the  workflow_dispatch:
+      # trigger may imply artifact publishing
       - cygwin.yml:144:9
       - cygwin.yml:151:9
       - cygwin.yml:158:9