Fix cookies with session lifetime #18820

Description:

As a regression from https://github.com/matomo-org/matomo/pull/18179 cookies with session lifetime don't work anymore.

As stated in the Cookie class an expire of 0 should indicate a session cookie:
https://github.com/matomo-org/matomo/blob/9c666ab8cf4c591ba26cd7d992972ef47d5369a2/core/Cookie.php#L81-L82

But that doesn't work anymore as the lifetime will be always converted to a datetime, resulting in 01-Jan-1970 00:00:00 UTC, causing the cookie to be never set.

fixes #18819

Review

• [ ] Functional review done
• [ ] Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done
• [ ] Wording review done
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] Documentation added if needed
• [ ] Existing documentation updated if needed