7.0.0: Drop PHP < 7.4, PHP 8.5

• Heads up: Dropped support for PHP < 7.4, see xp-framework/rfc#343,
  (@thekid)
• Added PHP 8.5 to test matrix, fix E_DEPRECATED: Using null as an array
  offset is deprecated, use an empty string instead - @thekid
• Heads up: Remove deprecated usage of calling Iteration::next()
  (@thekid)