vim-patch:9.1.2108: tests: Test_foldtextresult_rightleft() does not restore 'columns'

Problem:  Test_foldtextresult_rightleft() does not restore 'columns'
          (after v9.1.2102)
Solution: Save and restore the value of 'columns' (zeertzjq).

related: vim/vim#19220
closes:  vim/vim#19234

https://github.com/vim/vim/commit/4fcbc70fb1d7a6973edcd24f998990934b05893f

test/old/testdir/test_fold.vim

@@ -1334,6 +1334,7 @@ endfunc
 func Test_foldtextresult_rightleft()
   CheckFeature rightleft
 
+  let save_columns = &columns
   new
   set columns=70
   setlocal rightleft
@@ -1349,6 +1350,7 @@ func Test_foldtextresult_rightleft()
   call assert_equal('+--  2 lines: ' .. multibyte, foldtextresult(1))
 
   bw!
+  let &columns = save_columns
 endfunc
 
 " Test for merging two recursive folds when an intermediate line with no fold