Support reading values containing line separators

[Fallen-Breath]

If the properties files contains value containing line separators, e.g.:

abc=123
foo=bar\nbaz

The github action will fail, since the content format of the GITHUB_OUTPUT file cannot be recognized by the workflow

GITHUB_OUTPUT output with the current inplementation:

abc=123
foo=bar
baz

Expected GITHUB_OUTPUT output (using the method from github/docs#21529):

abc=123
foo<<DELIMITER
bar
baz
DELIMITER

Example implentation, just for a reference

fun packKeyValue(key: Any, value: Any): String {
    val s = value.toString()
    if (s.contains('\n') || s.contains('\r')) {
        var delimiter = "VALUE_DELIMITER"
        while (s.contains(delimiter)) {
            delimiter += "_X"
        }
        return "$key<<$delimiter${lineSeparator()}$s${lineSeparator()}$delimiter"
    } else {
        return "$key=$value"
    }
}

[madhead]

Hey, @Fallen-Breath, thanks for reporting! Could you please try the latest version (4.0.0)?