add checks for staff and system user before sending flags_agreed_and_post_deleted message

lib/post_destroyer.rb

@@ -196,7 +196,7 @@ class PostDestroyer
   end
 
   def agree_with_flags
-    if @post.is_flagged?
+    if @post.is_flagged? && @user.id > 0 && @user.staff?
       Jobs.enqueue(
         :send_system_message,
         user_id: @post.user.id,

spec/components/post_destroyer_spec.rb

@@ -566,9 +566,11 @@ describe PostDestroyer do
     let!(:bookmark) { PostAction.act(moderator, second_post, PostActionType.types[:bookmark]) }
     let!(:flag) { PostAction.act(moderator, second_post, PostActionType.types[:off_topic]) }
 
-    it "should delete public post actions and agree with flags" do
+    before do
       SiteSetting.queue_jobs = false
+    end
 
+    it "should delete public post actions and agree with flags" do
       second_post.expects(:update_flagged_posts_count)
 
       PostDestroyer.new(moderator, second_post).destroy
@@ -587,6 +589,23 @@ describe PostDestroyer do
       expect(notification).to be_present
       expect(notification.topic.title).to eq(I18n.t('system_messages.flags_agreed_and_post_deleted.subject_template'))
     end
+
+    it "should not send the flags_agreed_and_post_deleted message if it was deleted by system" do
+      second_post.expects(:update_flagged_posts_count)
+      PostDestroyer.new(Discourse.system_user, second_post).destroy
+      expect(
+        Topic.where(title: I18n.t('system_messages.flags_agreed_and_post_deleted.subject_template')).exists?
+      ).to eq(false)
+    end
+
+    it "should not send the flags_agreed_and_post_deleted message if it was deleted by author" do
+      SiteSetting.delete_removed_posts_after = 0
+      second_post.expects(:update_flagged_posts_count)
+      PostDestroyer.new(second_post.user, second_post).destroy
+      expect(
+        Topic.where(title: I18n.t('system_messages.flags_agreed_and_post_deleted.subject_template')).exists?
+      ).to eq(false)
+    end
   end
 
   describe "user actions" do