patch 9.0.0590: after exiting Insert mode spelling not checked in next line

Problem:    After exiting Insert mode spelling is not checked in the next
            line.
Solution:   When spelling is enabled redraw the next line after exiting Insert
            mode in case the spell highlight needs updating.
diff --git a/src/testdir/test_spell.vim b/src/testdir/test_spell.vim
index 3ea9aff..90c6d53 100644
--- a/src/testdir/test_spell.vim
+++ b/src/testdir/test_spell.vim
@@ -983,6 +983,10 @@
   let buf = RunVimInTerminal('-S XtestSpellCap', {'rows': 8})
   call VerifyScreenDump(buf, 'Test_spell_2', {})
 
+  " After adding word missing Cap in next line is updated
+  call term_sendkeys(buf, "3GANot\<Esc>")
+  call VerifyScreenDump(buf, 'Test_spell_3', {})
+
   " clean up
   call StopVimInTerminal(buf)
   call delete('XtestSpellCap')