ci.yml: use actions/checkout@v4

This addresses the following warning from GitHub Actions:

    Node.js 16 actions are deprecated. Please update the following
    actions to use Node.js 20: actions/checkout@v3. For more information
    see:
    https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

A near-identical warning forced everyone to upgrade to v3 last year, so
this is some pointless churn, but let's just get it over with again...

build(deps): bump golang.org/x/crypto from 0.13.0 to 0.17.0

Bumps [golang.org/x/crypto](https://github.com/golang/crypto) from 0.13.0 to 0.17.0.
- [Commits](https://github.com/golang/crypto/compare/v0.13.0...v0.17.0)

---
updated-dependencies:
- dependency-name: golang.org/x/crypto
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>