format timestamp as date to make it more easy to read in systemCheckPage #19256

Description:

Make it easier to read and understand when latest archiving was done.

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

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If you don't want this PR to be closed automatically in 28 days then you need to assign the label 'Do not close'.

Closing this PR. I'll cherry-pick and adjust the changes directly to 4.x-dev.