test: clean up dead/stale fixtures and bump test container images (#932)

Audit-driven cleanup of `act/` test fixtures. Three commits:

**1. Remove dead fixtures** — 12 fixture directories that no Go test references: `dir with spaces`, `environment-variables`, `issue-104`, `issue-122`, `issue-141`, `localdockerimagetest_`, `node`, `parallel`, `python`, `uses-composite-with-inputs`, `uses-composite-with-pre-and-post-steps`, `shells/custom` (under `act/runner/testdata/`), plus `act/artifactcache/testdata/example`.

**2. Collapse `actions/node{12,16,20}` to a single `actions/node24` fixture** — the trio dispatched through identical `IsNode()` code paths and exercised the container's node binary, not the `using:` string. Bumps bundled deps to current (`@actions/core@^3`, `@actions/github@^9`, `@vercel/ncc@^0.38.4`) — both runtime packages are now ESM-only, so `index.js` is rewritten to ESM and `"type": "module"` added. Drops committed `node_modules/` and `package-lock.json` (now gitignored locally; `dist/` continues to be ignored by the repo-root `.gitignore` as before). Reduces `local-action-js/push.yml` to a single `test-node24` job and bumps four other stale `using: node12/16` references in fixtures.

**3. Bump test container base images** to `node:24-bookworm-slim` / `node:24-bookworm` / `ubuntu:24.04`. Replaces `node:16-buster-slim`, `node:16-buster`, `node:12.20.1-buster-slim`, and the EOL `node:12-buster-slim` / `node:16-buster-slim` / `ubuntu:18.04` base images in `actions/{docker-local,docker-local-noargs,action1}/Dockerfile`.

The runner's model still accepts `using: node12/16/20` for third-party actions in the wild — those constants are untouched.

Fixes: https://gitea.com/gitea/runner/issues/931

---
This PR was written with the help of Claude Opus 4.7

Reviewed-on: https://gitea.com/gitea/runner/pulls/932
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

act/runner/testdata/basic/push.yml

@@ -11,7 +11,7 @@ jobs:
       - run: '[[ "$(pwd)" == "${GITHUB_WORKSPACE}" ]]'
       - run: echo ${{ env.TEST }} | grep value
       - run: env
-      - uses: docker://node:16-buster-slim
+      - uses: docker://node:24-bookworm-slim
         with:
           somekey: ${{ env.TEST }}
           args: echo ${INPUT_SOMEKEY} | grep somevalue
@@ -31,10 +31,10 @@ jobs:
     runs-on: ubuntu-latest
     needs: [build]
     steps:
-      - uses: docker://node:16-buster-slim
+      - uses: docker://node:24-bookworm-slim
         with:
           args: env
-      - uses: docker://node:16-buster-slim
+      - uses: docker://node:24-bookworm-slim
         with:
           entrypoint: /bin/echo
           args: ${{github.event_name}}