patch 8.2.3467: CursorHoldI event interferes with "CTRL-G U"

Problem:    CursorHoldI event interferes with "CTRL-G U". (Naohiro Ono)
Solution:   Restore the flag for "CTRL-G U" after triggering CursorHoldI.
            (closes #8937)

src/edit.c

@@ -1057,6 +1057,9 @@ doESCkey:
 	case K_CURSORHOLD:	// Didn't type something for a while.
 	    ins_apply_autocmds(EVENT_CURSORHOLDI);
 	    did_cursorhold = TRUE;
+	    // If CTRL-G U was used apply it to the next typed key.
+	    if (dont_sync_undo == TRUE)
+		dont_sync_undo = MAYBE;
 	    break;
 
 #ifdef FEAT_GUI_MSWIN

src/testdir/test_autocmd.vim

@@ -100,6 +100,22 @@ if has('timers')
     set updatetime&
   endfunc
 
+  func Test_cursorhold_insert_ctrl_g_U()
+    au CursorHoldI * :
+    set updatetime=20
+    new
+    call timer_start(100, { -> feedkeys("\<Left>foo\<Esc>", 't') })
+    call feedkeys("i()\<C-g>U", 'tx!')
+    sleep 200m
+    call assert_equal('(foo)', getline(1))
+    undo
+    call assert_equal('', getline(1))
+
+    bwipe!
+    au! CursorHoldI
+    set updatetime&
+  endfunc
+
   func Test_OptionSet_modeline()
     call test_override('starting', 1)
     au! OptionSet

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3467,
 /**/
     3466,
 /**/