Make bson-enum_error resilient to PHP 8.6 interface handler order

[GromNaN]

Backport of #1953 to v2.2.

PHP is calling the interface_gets_implemented handlers in a different order since php/php-src#18622

The Persistable interface extends Unserializable which is the one that cannot be implemented.

[Copilot]

Pull request overview

Updates BSON enum error PHPT expectations to tolerate PHP 8.6’s changed interface_gets_implemented handler order, where enums attempting to implement MongoDB\BSON\Persistable may now fail against either Persistable or its parent Unserializable.

Changes:

• Switch PHPT expectations from --EXPECTF-- to --EXPECTREGEX-- for the relevant enum/Persistable error tests.
• Accept either MongoDB\BSON\Persistable or MongoDB\BSON\Unserializable in the fatal error message to keep tests stable across PHP versions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tests/bson/bson-enum_error-003.phpt	Makes expected fatal error resilient to interface handler order by matching Persistable or Unserializable.
tests/bson/bson-enum_error-004.phpt	Same resilience update for backed enums implementing Persistable.

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