chore: bump action runtime to Node 24

Resolves #448. GitHub is forcing all Node 20 JavaScript actions onto
Node 24 on June 2nd 2026 and surfacing a deprecation annotation on
every run in the meantime. Bumping `runs.using` from `node20` to
`node24` in action.yml silences the warning and gets ahead of the
forced cutover.

Scope is deliberately minimal:

- Only `action.yml` changes.
- `npm run build` reruns cleanly and produces a byte-identical
  `bin/action.min.js` (the runtime declaration does not affect the
  microbundle output target, which is already `--target node`).
- `npm run format:check` clean. `npm run test` — 13 passed, 0 failed.
- No source, dependency, or API changes.

Only the action runtime is touched; consumers do not need to update
their workflows.

Author: MukundaKatta

action.yml

@@ -19,7 +19,7 @@ branding:
   icon: "globe"
   color: "blue"
 runs:
-  using: "node20"
+  using: "node24"
   main: "bin/action.min.js"
 inputs:
   repoToken: