patch 8.2.4152: block insert with double wide character fails

Problem:    Block insert with double wide character fails.
Solution:   Adjust the expected output.
diff --git a/src/testdir/test_utf8.vim b/src/testdir/test_utf8.vim
index 0210ce6..862e73b 100644
--- a/src/testdir/test_utf8.vim
+++ b/src/testdir/test_utf8.vim
@@ -8,7 +8,7 @@
   new
   call setline(1, ["aaa", "あああ", "bbb"])
   exe ":norm! gg0l\<C-V>jjIx\<Esc>"
-  call assert_equal(['axaa', 'xあああ', 'bxbb'], getline(1, '$'))
+  call assert_equal(['axaa', ' xあああ', 'bxbb'], getline(1, '$'))
   bwipeout!
 endfunc