patch 8.2.0040: timers test is still flaky on Travis for Mac

Problem:    Timers test is still flaky on Travis for Mac.
Solution:   Run separately instead of as part of test_alot.
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index fab1460..2cccc8e 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -429,6 +429,7 @@
 	test_textformat.res \
 	test_textobjects.res \
 	test_textprop.res \
+	test_timers.res \
 	test_trycatch.res \
 	test_undo.res \
 	test_user_func.res \