patch 9.0.0559: timer test may get stuck at hit-enter prompt

Problem:    Timer test may get stuck at hit-enter prompt.
Solution:   Feed some more characters.

src/testdir/test_timers.vim

@@ -379,11 +379,13 @@ func Test_nocatch_timer_garbage_collect()
     let a = {'foo', 'bar'}
   endfunc
   func FeedChar(id)
-    call feedkeys('x', 't')
+    call feedkeys(":\<CR>", 't')
   endfunc
   call timer_start(300, 'FeedChar')
   call timer_start(100, 'CauseAnError')
-  let x = getchar()
+  let x = getchar()   " wait for error in timer
+  let x = getchar(0)  " read any remaining chars
+  let x = getchar(0)
 
   set ut&
   call test_override('no_wait_return', 1)

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    559,
 /**/
     558,
 /**/