vim-patch:9.1.0415: Some functions are not tested

Problem:  Some functions are not tested
Solution: Add a few more tests, fix a few minor problems
          (Yegappan Lakshmanan)

closes: vim/vim#14789

fe424d13ef

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

test/old/testdir/test_vimscript.vim

@@ -7449,6 +7449,13 @@ func Test_for_over_string()
     let res ..= c .. '-'
   endfor
   call assert_equal('', res)
+
+  " Test for ignoring loop var assignment
+  let c = 0
+  for _ in 'abc'
+    let c += 1
+  endfor
+  call assert_equal(3, c)
 endfunc
 
 " Test for deeply nested :source command  {{{1