patch 9.0.0839: test may fail depending on sequence of events

Problem:    Test may fail depending on sequence of events.
Solution:   Accept error codes in either order. (Yee Cheng Chin,
            closes #11510)

src/testdir/test_vim9_script.vim

@@ -4087,7 +4087,8 @@ def Test_no_unknown_error_after_error()
       endfor
   END
   writefile(lines, 'Xdef', 'D')
-  assert_fails('so Xdef', ['E684:', 'E1012:'])
+  # Either the exit or out callback is called first, accept them in any order
+  assert_fails('so Xdef', ['E684:\|E1012:', 'E1012:\|E684:'])
 enddef
 
 def InvokeNormal()

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    839,
 /**/
     838,
 /**/