2.1.0: Intersection types

• Emit $expr is mixed as true, making it effectively a wildcard as
  seen in https://wiki.php.net/rfc/pattern-matching
  (@thekid)
• Added support for intersection types, e.g. Runnable|IteratorAggregate
  (@thekid)
• Added PHP 8.5 and 8.6 to the test matrix following the PHP 8.5 release
  (@thekid)