Update GitHub actions (versions / ergonomics).

This change set bumps the referenced / reusable GitHub actions to their
latest versions, bumps node versions, and enables reuse of a “test” wf.

.github/workflows/check-branch.yml

@@ -0,0 +1,6 @@
+# Run tests on pushes to all branches.
+name: Check Branch
+on: [push]
+jobs:
+  test:
+    uses: Netflix/x-element/.github/workflows/test.yml

.github/workflows/publish-to-npm.yml

@@ -0,0 +1,21 @@
+# Publish package to npm whenever a release is pushed.
+# See https://docs.github.com/en/actions/publishing-packages/publishing-nodejs-packages
+name: Publish to npm
+on:
+  release:
+    types: [published]
+jobs:
+  test:
+    uses: Netflix/x-element/.github/workflows/test.yml
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v3
+        with:
+          node-version: '20.x'
+          registry-url: 'https://registry.npmjs.org'
+      - run: npm ci
+      - run: npm publish
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}

.github/workflows/push.yml → .github/workflows/test.yml

@@ -1,17 +1,17 @@
-name: Push
-on: [push]
+name: Test
+on: [workflow_call]
 jobs:
   test:
     runs-on: ubuntu-latest
     permissions:
       contents: read
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-node@v2
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v3
         with:
-          node-version: '18.x'
+          node-version: '20.x'
           registry-url: 'https://registry.npmjs.org'
-      - run: npm install
+      - run: npm ci
       - run: npm run lint
       - run: npm start &
       - run: sleep 2