Add sub issue list support (#32940)

Just like GitHub, show issue icon/title when the issue number is in a list

services/markup/main_test.go

@@ -11,6 +11,6 @@ import (
 
 func TestMain(m *testing.M) {
 	unittest.MainTest(m, &unittest.TestOptions{
-		FixtureFiles: []string{"user.yml", "repository.yml", "access.yml", "repo_unit.yml"},
+		FixtureFiles: []string{"user.yml", "repository.yml", "access.yml", "repo_unit.yml", "issue.yml"},
 	})
 }