Fix flaky test in dashboard/snippets_spec.rb

Similar to https://gitlab.com/gitlab-org/gitlab/-/issues/206937, this
test was flaky due to the image lazy loader. The test is asserting on
the image src, but it fails when the src value is still the lazy
loader's placeholder image.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/216541

spec/features/dashboard/snippets_spec.rb

@@ -35,7 +35,7 @@ describe 'Dashboard snippets' do
       element = page.find('.row.empty-state')
 
       expect(element).to have_content("Code snippets")
-      expect(element.find('.svg-content img')['src']).to have_content('illustrations/snippets_empty')
+      expect(element.find('.svg-content img.js-lazy-loaded')['src']).to have_content('illustrations/snippets_empty')
     end
 
     it 'shows new snippet button in main content area' do