Fix JobDispatcher crash during force cancellation.

[TingluoHuang]

The JobDispatcher will crash in this scenario:

• Job A lands on runner
• Runner start worker process
• Job A finish on worker process, but somehow the worker process didn't exit fast enough
• Job B lands on the runner
• Runner noticed worker process for Job A is still running, so it try to cancel and gracefully shutdown the worker process by sending a cancellation message via AnonymousPipe
• Worker process exit right before runner try to cancel it.
• The message sending to AnonymousPipe failed since the worker exited, exception get thrown and crashed the JobDispatcher

The fix: add another catch(Exception) to make sure the failure on sending cancellation don't crash the JobDispatcher.

https://github.com/github/c2c-actions-support/issues/3423