patch 8.2.4601: Vim9: not enough test coverage for executing :def function

Problem:    Vim9: not enough test coverage for executing :def function.
Solution:   Add a few more tests.
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index c94f298..3e4e9a4 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -2003,6 +2003,12 @@
       endfor
       assert_equal(6, total)
 
+      total = 0
+      for b in 0z010203
+        total += b
+      endfor
+      assert_equal(6, total)
+
       var chars = ''
       for s: string in 'foobar'
         chars ..= s