Increase async timeout for Run main program task from 2100s to 3600s

Previous run hit the 35min (2100s) wall exactly: task started 08:47:29,
timed out at 09:22:37. Successful runs complete in ~45min total with
the main program taking ~37min. Raise to 3600s (60min) for headroom.

Author: szachovy

tests/testsuite/roles/testing/tasks/system.yml

@@ -13,7 +13,7 @@
   args:
     executable: "/bin/bash"
     chdir: "../../"
-  async: 2100
+  async: 3600
   poll: 60
   register: "run_command"
   changed_when: false