Replace deprecated set-output with GITHUB_OUTPUT and bump Node runtime to node24

[jmklix]

Summary

• Bumps @actions/core ^1.9.1 → ^1.10.1 so core.setOutput writes to $GITHUB_OUTPUT instead of emitting the deprecated ::set-output workflow command.
• Bumps action.yml runtime node12 → node24 (Node 12 and Node 16 are both EOL on GitHub Actions).
• Bumps @actions/github ^5.0.0 → ^6.0.0 (dropped legacy transitive undici) and @vercel/ncc ^0.31.1 → ^0.38.1 (0.31 fails under modern Node's OpenSSL, so the bundle could not otherwise be regenerated).
• Regenerated dist/index.js and dist/LICENSE.md via npm run build; verified setOutput now writes to $GITHUB_OUTPUT.

No source (src/*.ts) changes were needed — the fix is entirely in the pinned dependency versions and the runtime declaration.

Fixes #42.

Test plan

• npm test — 41/41 pass, lint clean
• grep -n "GITHUB_OUTPUT" dist/index.js — confirms the new code path
• Consumer smoke test: run this branch of the action against a test issue on a downstream repo (e.g. aws/aws-cdk's issue-label-assign.yml workflow) and confirm no set-output deprecation warnings appear in the run log