patch 8.2.0475: channel out_cb test still fails sometimes on Mac

Problem:    Channel out_cb test still fails sometimes on Mac.
Solution:   Use an ever longer timeout.

src/testdir/test_channel.vim

@@ -1174,8 +1174,13 @@ func Test_out_cb()
     " Receive a json object split in pieces
     let g:Ch_outobj = ''
     call ch_sendraw(job, "echosplit [0, {\"one\": 1,| \"tw|o\": 2, \"three\": 3|}]\n")
-    " For unknown reason this can be very slow on Mac.
-    call WaitForAssert({-> assert_equal({'one': 1, 'two': 2, 'three': 3}, g:Ch_outobj)}, 10000)
+    " For unknown reasons this can be very slow on Mac.
+    if has('mac')
+      let timeout = 20000
+    else
+      let timeout = 5000
+    endif
+    call WaitForAssert({-> assert_equal({'one': 1, 'two': 2, 'three': 3}, g:Ch_outobj)}, timeout)
   finally
     call job_stop(job)
   endtry

src/version.c

@@ -738,6 +738,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    475,
 /**/
     474,
 /**/