👷 Modernize release workflow runtime

[AnandChowdhary]

Summary

• update the release job from the retired Ubuntu 18.04 runner to ubuntu-latest
• update actions/cache from v2 to v6 (Node 24 runtime)
• supersede Dependabot PR ⬆️ Bump actions/cache from 2 to 6 #161 with a branch based on current master

Why

The one-line cache update in #161 is clean, but actionlint shows the surrounding release job still targets the unsupported ubuntu-18.04 label. Updating both together keeps the new Node 24 action on a current runner and makes the release workflow runnable again.

Test plan

• YAML parse
• actionlint on .github/workflows/release.yml
• Node 14.21.3 / npm 6.14.18 npm ci
• Jest (2 suites / 2 tests)
• TypeScript build
• ncc package build
• npm pack --dry-run
• staged diff and added-line security scan

Supersedes #161.