fix(ci): bump node version to 20 in integrity-check

yargs@18.0.0 requires Node >=20.19.0, so Node 18 is no longer
compatible.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: frostebite

.github/workflows/integrity-check.yml

@@ -24,7 +24,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: '18'
+          node-version: '20'
       - run: yarn
       - run: yarn lint
       - run: yarn test:ci --coverage