Re-work test_lowlevel_error_message test

[dentarg]

Feedback from #2607 (comment)

puma/test/test_puma_server.rb

Lines 359 to 362 in 0a149ec

	# will raise fatal: machine stack overflow in critical region
	obj = {}
	obj['cycle'] = obj
	::JSON.dump(obj)

I think this is not a reliable test for this issue because:

• Not all Ruby implementations might expose no backtrace for a stack overflow (that's pretty unhelpful, isn't it?)
• a stack overflow is a regular exception but given it messes the VM badly you can consider the VM corrupted after it, so maybe stack overflows should become fatal in the future, since it's very rarely safe to rescue it (you would need no ensure and no finally in the VM, and no second stack overflow while handling the stack overflow very close to the limit, and probably other things which cannot be guaranteed)
• More details on Use the bundler shipped with ruby for non-MRI #2811

Maybe we can just test creating an exception and using set_backtrace(nil)?