Bump deprecated GitHub Actions versions

- actions/checkout@v3 -> @v4 in docker.yml
- actions/setup-node@v1 -> @v4 in ci.yml (both jobs that use it)
- Replace deprecated `::set-output` with $GITHUB_OUTPUT in the
  ESLint yarn-cache-dir step

The remaining Node 20 deprecation warnings on actions/cache@v4,
actions/checkout@v4, and the docker/* actions will resolve once
upstream ships Node 24 builds; not blocking, the runtime won't
flip until 2026-06.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -60,12 +60,12 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Install Node.js
-        uses: actions/setup-node@v1
+        uses: actions/setup-node@v4
         with:
           node-version: 20.19.0
       - name: Cache directory path
         id: yarn-cache-dir-path
-        run: echo "::set-output name=dir::$(yarn cache dir)"
+        run: echo "dir=$(yarn cache dir)" >> "$GITHUB_OUTPUT"
       - uses: actions/cache@v4
         id: yarn-cache
         with:
@@ -134,7 +134,7 @@ jobs:
         with:
           ruby-version: 4.0.1
       - name: Set up Node
-        uses: actions/setup-node@v1
+        uses: actions/setup-node@v4
         with:
           node-version: 20.19.0
       - name: Install Chrome

.github/workflows/docker.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         submodules: recursive