FIX: do not show send pm prompt when user cant pm (discourse#25912)

Prior to this fix even when the user was not part of a group allowing sending pm we would show the prompt: "You've replied to ... X times, did you know you could send them a personal message instead?"

lib/composer_messages_finder.rb

@@ -181,6 +181,7 @@ def check_dominating_topic
   end
 
   def check_get_a_room(min_users_posted: 5)
+    return unless @user.guardian.can_send_private_messages?
     return unless educate_reply?(:notified_about_get_a_room)
     return unless @details[:post_id].present?
     return if @topic.category&.read_restricted

spec/lib/composer_messages_finder_spec.rb

@@ -441,6 +441,23 @@
       SiteSetting.educate_until_posts = 10
       user.stubs(:post_count).returns(11)
       SiteSetting.get_a_room_threshold = 2
+      SiteSetting.personal_message_enabled_groups = Group::AUTO_GROUPS[:everyone]
+    end
+
+    context "when user can't send private messages" do
+      fab!(:group) { Fabricate(:group) }
+      before { SiteSetting.personal_message_enabled_groups = group.id }
+
+      it "does not show the message" do
+        expect(
+          ComposerMessagesFinder.new(
+            user,
+            composer_action: "reply",
+            topic_id: topic.id,
+            post_id: op.id,
+          ).check_get_a_room(min_users_posted: 2),
+        ).to be_blank
+      end
     end
 
     it "does not show the message for new topics" do