`/\d+ warnings? emitted/` warning is not ignored

[DaniPopes]

ui_test currently skips only the aborting due to \d+ previous errors? diagnostic:

ui_test/src/diagnostics/rustc.rs

Lines 45 to 52 in a846e59

	// All other messages go into the general bin, unless they are specifically of the
	// "aborting due to X previous errors" variety, as we never want to match those. They
	// only count the number of errors and provide no useful information about the tests.
	} else if !(msg.message.starts_with("aborting due to")
	&& msg.message.contains("previous error"))
	{
	messages_from_unknown_file_or_line.push(msg);
	}

When 0 errors, >0 warnings are emitted, rustc will also emit another warning with /\d+ warnings? emitted/ as the message, but this is not ignored by ui_test like the error one

Relevant code in rustc's compiletest: https://github.com/rust-lang/rust/blob/3ef8e64ce9f72ee8d600d55bc43b36eed069b252/src/tools/compiletest/src/json.rs#L223-L232