Update for Fastify v5

[synapse]

Ref: fastify/fastify#5116

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

CC @simoneb

[simoneb]

For some reason I cannot create a next branch in this repo, I assume the permissions are not configured correctly hence my membership to the org doesn't give me access.

[gurgunday]

@fastify/leads can you give @fastify/libraries access to this repo?

[mcollina]

Access was granted last week