fix test that fails due to 100ms timeout

A test that sometimes fails to finish within 100ms failed again. See:

https://github.com/apache/daffodil/runs/4096774542?check_suite_focus=true
https://github.com/apache/daffodil/runs/4107338275?check_suite_focus=true

[error] Test org.apache.daffodil.api.TestParseIndividualMessages.testDaffodilParseFromNetworkDelimited2b failed: java.util.concurrent.TimeoutException: Futures timed out after [100 milliseconds], took 0.476 sec [0.872 sec]

This test should be redesigned so as to not-need a timeout. In principle this timeout indicates that something could be broken. But most likely it's just that the test machine is heavily overloaded and so these take longer than 100ms.