runtime: don't check the exit code in TestWERDialogue
TestWERDialogue intent is to check that the WER dialog doesn't pop-up
when `GOTRACEBACK=wer` is set. CL 474915 extended the test to also
check the error code of the crashed process. This change is causing
failures in Microsoft internal test pipelines because some WER setups
can modify the exit code of the crashed application, for example to
signal that the crash dump has been collected.
Fix this issue by not checking the error code in TestWERDialogue. Also,
add a new test, TestCrashExitCode, which does the same but using
`GOTRACEBACK=crash` instead, so that we have one test that checks the
error code.