Review third-party PHP 8.4 deprecations before 6.0.0-rc1

[emteknetnz]

Background #331 (comment)

Review the deprecation warnings in CI before we release 6.0.0-rc1 in case we need to do some forking or replace a dependency, or at the very least so that we can provide appropriate comms to indicate that while our codebase has been updated, some upstream dependencies are known to not have done so yet.

Notes

• onelogin/php-saml just needs release
• sensiolabs/ansi-to-html just needs release
• Some PRs below are for webauthn-authenticator which is no longer supported though is a dev-dependency in sink

PRs

• Make nullable parameter explicity nullable for PHP 8.4 aws/aws-sdk-php#3043
• Make nullable parameters explicity nullable for PHP 8.4 oscarotero/Embed#551
• Make nullable parameters explicity nullable for PHP 8.4 lanthaler/JsonLD#112
• Make nullable parameters explicity nullable for PHP 8.4 reactphp/child-process#111
• Make nullable parameters explicity nullable for PHP 8.4 Spomky-Labs/pki-framework#59
• Make nullable parameters explicity nullable for PHP 8.4 ua-parser/uap-php#79
• Make nullable parameters explicity nullable for PHP 8.4 web-auth/webauthn-framework#662