chore(deps): bump GitHub Actions to latest versions
- actions/checkout: v4 -> v6.0.2 (codeberg-mirror, rust, security-audit, nix)
- actions/upload-artifact: v7.0.0 -> v7.0.1
- codecov/codecov-action: v4 -> v6.0.0 (rename file -> files input)
- DeterminateSystems/magic-nix-cache-action: v7 -> v13
- DeterminateSystems/nix-installer-action: v12 -> v22
- release-plz/action: v0.5.127 -> v0.5.128
- Swatinem/rust-cache: v2 -> v2.9.1
Resolves Node 20 deprecation warnings for actions that have shipped
Node 24 releases. snapcore/action-build and snapcore/action-publish
remain on node20 upstream; magic-nix-cache-action also stays on node20
(no Node 24 release yet). Validated locally with act on rust.yml.