vim-patch:8.2.4121: Visual test fails on MS-Windows

Problem:    Visual test fails on MS-Windows.
Solution:   Set 'isprint' so that the character used is not printable.
262898ae43

src/nvim/testdir/test_visual.vim

@@ -1249,11 +1249,13 @@ endfunc
 
 func Test_visual_block_append_invalid_char()
   " this was going over the end of the line
+  set isprint=@,161-255
   new
   call setline(1, ['	   let xxx', 'xxxxxˆ', 'xxxxxxxxxxx'])
   exe "normal 0\<C-V>jjA-\<Esc>"
   call assert_equal(['	-   let xxx', 'xxxxx   -ˆ', 'xxxxxxxx-xxx'], getline(1, 3))
   bwipe!
+  set isprint&
 endfunc
 
 func Test_visual_reselect_with_count()