patch 8.2.4921: spell test fails because of new illegal byte check

Problem:    Spell test fails because of new illegal byte check.
Solution:   Remove the test.

src/testdir/test_spell.vim

@@ -877,14 +877,6 @@ func Test_spell_screendump()
   call delete('XtestSpell')
 endfunc
 
-func Test_spell_single_word()
-  new
-  silent! norm 0R00
-  spell! <20><>
-  silent 0norm 0r$ Dvz=
-  bwipe!
-endfunc
-
 let g:test_data_aff1 = [
       \"SET ISO8859-1",
       \"TRY esianrtolcdugmphbyfvkwjkqxz-\xEB\xE9\xE8\xEA\xEF\xEE\xE4\xE0\xE2\xF6\xFC\xFB'ESIANRTOLCDUGMPHBYFVKWJKQXZ",

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4921,
 /**/
     4920,
 /**/