Replace silverstripe/closure with laravel/serializable-closure

[GuySartorelli]

https://github.com/silverstripe/closure/ was forked from https://github.com/opis/closure to address PHP compatibility concerns.

https://github.com/laravel/serializable-closure is a fork of the same repo, which is well maintained. It was a recommended replacement in opis/closure#145 (comment)

We should swap to using laravel/serializable-closure

Since they're both forks of the same package I think this could be sensibly done in a minor release.

Acceptance Criteria

• Anywhere using silverstripe/closure as a dependency uses laravel/serializable-closure instead
• silverstripe/closure is archived in GitHub
• silverstripe/closure is marked abandoned in Packagist with the recommendation to use laravel/serializable-closure instead

PRs

• ENH Add silverstripe/doorman supported-modules#49
• ENH Fallback to reading PHP version from composer.json gha-generate-matrix#115
• ENH CMS 6 compatibility doorman#49
• DEP Use CMS 6 version of asyncphp/doorman symbiote/silverstripe-queuedjobs#454
• MNT Add archive notice closure#5

[emteknetnz]

The doorman runner in queuedjobs was the only place in sink that I could find usage of silverstripe/closure

[GuySartorelli]

Assigning back to Steve to tag doorman

[GuySartorelli]

PRs merged. Reassigning to Steve for any other ACs that need to be done

[emteknetnz]

All done