patch 8.1.0533: screendump tests can be flaky

Problem:    Screendump tests can be flaky.
Solution:   Add VerifyScreenDump to the pattern of flaky tests.

Author: brammool

src/testdir/runtest.vim

@@ -330,7 +330,7 @@ let s:flaky_tests = [
       \ ]
 
 " Pattern indicating a common flaky test failure.
-let s:flaky_errors_re = 'StopVimInTerminal'
+let s:flaky_errors_re = 'StopVimInTerminal\|VerifyScreenDump'
 
 " Locate Test_ functions and execute them.
 redir @q

src/version.c

@@ -792,6 +792,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    533,
 /**/
     532,
 /**/