patch 8.1.2290: autocommand test fails

Problem:    Autocommand test fails.
Solution:   Remove 'closeoff' from 'diffopt'.

src/testdir/test_autocmd.vim

@@ -1157,6 +1157,7 @@ func Test_OptionSet_diffmode_close()
   call setline(1, ['buffer 2', 'line 2', 'line 3', 'line4'])
   call assert_fails(':diffthis', 'E788')
   call assert_equal(1, &diff)
+  set diffopt-=closeoff
   bw!
   call assert_fails(':diffoff!', 'E788')
   bw!

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2290,
 /**/
     2289,
 /**/