Update WP background processing and Action Scheduler

[remyperona]

Description

Update our processing libraries to their latest versions

Type of change

• Enhancement (non-breaking change which improves an existing functionality).

Checklists

Generic development checklist

• My code follows the style guidelines of this project, with adapted comments and without new warnings.
• I have added unit and integration tests that prove my fix is effective or that my feature works.
• The CI passes locally with my changes (including unit tests, integration tests, linter).

Test summary

• I triggered all changed lines of code at least once without new errors/warnings/notices.