CI: Split .github\workflows\ci.yml into separate workflows

[simonjayhawkins]

CI / Checks (push) — Checks and CI / Web and docs (push) — Web and docs are part of the same workflow.

If we want to restart one of the jobs (quiet infrequent - a few instances of connection issues on web and docs IIRC), both are re-run.

It may make sense to split these.

An alternative could be to combine with pre-commit into a single workflow and only run 'Checks' and 'Web and docs' on success.