patch 8.2.4293: Vim9: when copying a list it gets type list<any>

Problem:    Vim9: when copying a list it gets type list<any> even when the
            original list did not have a type.
Solution:   Only set the type when the original list has a type. (closes #9692)
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index c6466d3..a4e3e9e 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -1495,6 +1495,9 @@
 
       # result of glob() is "any", runtime type check
       var sl: list<string> = glob('*.txt', false, true) + ['']
+
+      var lln: list<list<number>> = [[1] + [2]]
+      assert_equal([[1, 2]], lln)
   END
   v9.CheckDefAndScriptSuccess(lines)
 enddef