Support for HTTP-date in HTTP Retry-After Header (RFC9110)

[Raighar]

According to RFC9110 (https://httpwg.org/specs/rfc9110.html#field.retry-after) the Retry-After Header supports two types of value: HTTP-date and delay-seconds.
When the field contains a http-date, the check crashes and falls back to the default of 2 seconds sleep:

.acme.sh/acme.sh: line 5875: [: Thu,20Aug202609: integer expression expected

I'd be happy to provide a pull request if you'd like.

Thanks!

[github-actions]

Please upgrade to the latest code and try again first. Maybe it's already fixed. acme.sh --upgrade If it's still not working, please provide the log with --debug 2, otherwise, nobody can help you. Before posting the log, review it and REDACT any secrets: private keys (-----BEGIN ... PRIVATE KEY----- blocks), API tokens and passwords.