Use artifact caching for phpcs

Problem/Motivation

See 📌 Use artifacts to share the eslint and styleint caches from core to MRs Needs review and 📌 Try to store the phpstan result cache as an artifact Active .

phpcs supports caching, so we should be able to re-use a similar approach from the previous two MRs for the phpcs job too. The job currently completes very quickly, but it requires 16 CPUs - so the goal should be the same speed but with more like 4 CPUs.

I had a quick go at this in a sandbox branch, but got script timeouts, so going to wait for the other two MRs to land before trying properly.

Steps to reproduce

Proposed resolution

Remaining tasks

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Introduced terminology

API changes

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Release notes snippet