Improve img lazy loading (#34804)

Related #32051 and #13526

services/mailer/mail_test.go

@@ -528,7 +528,7 @@ func TestEmbedBase64Images(t *testing.T) {
 		require.NoError(t, err)
 
 		mailBody := msgs[0].Body
-		assert.Regexp(t, `MSG-BEFORE <a[^>]+><img src="data:image/png;base64,iVBORw0KGgo="/></a> MSG-AFTER`, mailBody)
+		assert.Regexp(t, `MSG-BEFORE <a[^>]+><img src="data:image/png;base64,iVBORw0KGgo=".*/></a> MSG-AFTER`, mailBody)
 	})
 
 	t.Run("EmbedInstanceImageSkipExternalImage", func(t *testing.T) {