Only enable 'trap' for new enough harnesses.

The 'trap' option was added to TAP::Harness version 3.22. Attempting to set it
on earlier versions is a fatal error, and aborts testing. Hence pass
argument conditionally, based on $TAP::Harness::VERSION.

Signed-off-by: Moritz Lenz <moritz@faui2k3.org>

t/harness

@@ -124,7 +124,7 @@ if (eval "require $tap_harness_class;") {
         jobs        => $jobs,
         ignore_exit => 1,
         merge       => 1,
-        trap        => 1,
+        $TAP::Harness::VERSION > 3.21 ? (trap => 1) : (),
         $archive ? ( archive => $archive ) : (),
         $extra_properties ? ( extra_properties => $extra_properties ) : (),
     );