Fix false-negative goal absence assertion

The selector `.d-block.color-fg-muted` never matched anything because
the goal element uses neither `d-block` nor that class combination.
Asserts against the goal element's DOM id instead.

Author: myabc

modules/backlogs/spec/components/backlogs/sprint_component_spec.rb

@@ -262,7 +262,7 @@ def menu_items
 
       context "when the sprint has no goal for the project" do
         it "does not render goal text" do
-          expect(rendered_component).to have_no_css(".d-block.color-fg-muted")
+          expect(rendered_component).to have_no_css("#sprint_#{sprint.id}_goal")
         end
 
         it "does not describe the sprint heading" do