patch 9.0.0257: "->" in ":scriptnames" output not tested yet

Problem:    "->" in ":scriptnames" output not tested yet.
Solution:   Add a check.
diff --git a/src/testdir/test_vim9_import.vim b/src/testdir/test_vim9_import.vim
index 5c14b05..d9b40d6 100644
--- a/src/testdir/test_vim9_import.vim
+++ b/src/testdir/test_vim9_import.vim
@@ -2942,6 +2942,11 @@
     assert_equal(1, len(infoTo))
     assert_equal(1, len(infoFrom))
     assert_equal(infoTo[0].sid, infoFrom[0].sourced)
+    var output: string
+    redir => output
+    scriptnames
+    redir END
+    assert_match(infoFrom[0].sid .. '->' .. infoFrom[0].sourced .. '.*Xfrom', output)
 
     unlet g:resultFunc
     unlet g:resultValue