Change date_updated only when content changed

[DL6ER]

What does this implement/fix?

@yubiuser noted in # that the timestamp should not be updated when the list's content hasn't changed. We realize this by adding an additional condition into the SQL UPDATE statement.

To work, this depends on the related core PR pi-hole/pi-hole#5872

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Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): N/A

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