patch 9.0.0608: with spelling, deleting a full stop does not update next line

Problem:    With spell checking, deleting a full stop at the end of a line
            does not update SpellCap at the start of the next line.
Solution:   Update the next line when characters have been deleted.  Also when
            using undo.
diff --git a/src/testdir/test_spell.vim b/src/testdir/test_spell.vim
index 90c6d53..3712b54 100644
--- a/src/testdir/test_spell.vim
+++ b/src/testdir/test_spell.vim
@@ -987,6 +987,14 @@
   call term_sendkeys(buf, "3GANot\<Esc>")
   call VerifyScreenDump(buf, 'Test_spell_3', {})
 
+  " Deleting a full stop removes missing Cap in next line
+  call term_sendkeys(buf, "5Gddk$x")
+  call VerifyScreenDump(buf, 'Test_spell_4', {})
+
+  " Undo also updates the next line (go to command line to remove message)
+  call term_sendkeys(buf, "u:\<Esc>")
+  call VerifyScreenDump(buf, 'Test_spell_5', {})
+
   " clean up
   call StopVimInTerminal(buf)
   call delete('XtestSpellCap')