Disable Generate Suggestion on private changes

Don't send requests for generating suggestion on private changes.

Release-Notes: skip
Google-Bug-Id: b/312228673
Change-Id: Id5e14adb84fbb5e1397e3b0e554ab293b08fa5ce

polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts

diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
index 2dfca5c..21bf50e 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
@@ -973,7 +973,8 @@
         )) &&
       this.comment === this.comments?.[0] && // Is first comment
       (this.comment.range || this.comment.line) && // Disabled for File comments
-      !hasUserSuggestion(this.comment)
+      !hasUserSuggestion(this.comment) &&
+      this.getChangeModel().getChange()?.is_private !== true
     );
   }