Use Node.js 22 in CI workflows

Node.js 20 reaches EOL on 2026-04-30. Switch to Node.js 22 LTS
which is supported until 2027-04-30.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hsbt

.github/workflows/ci.yml

@@ -32,7 +32,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@53b83947a5a98c8d113130e565377fae1a50d02f # v6.3.0
         with:
-          node-version: '20'
+          node-version: '22'
           cache: 'npm'
       - name: Install npm dependencies
         run: npm ci

.github/workflows/jekyll.yml

@@ -30,7 +30,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@53b83947a5a98c8d113130e565377fae1a50d02f # v6.3.0
         with:
-          node-version: '20'
+          node-version: '22'
           cache: 'npm'
       - name: Install npm dependencies
         run: npm ci