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

Problem:    "->" in ":scriptnames" output not tested yet.
Solution:   Add a check.

src/testdir/test_vim9_import.vim

@@ -2942,6 +2942,11 @@ def Test_vim9_import_symlink()
     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

src/version.c

@@ -731,6 +731,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    257,
 /**/
     256,
 /**/