cryptography高版本兼容问题：日期时间带时区信息的比较

[gtwww]

当 cryptography==42.0.3 版本较高时，会报：

CryptographyDeprecationWarning: Properties that return a naïve datetime object have been deprecated. Please switch to not_valid_before_utc.

改用：datetime.now(timezone.utc)与certificate.not_valid_before_utc进行比较。