Install yarn

See actions/setup-node#182

Author: BlakeRain

.github/workflows/deploy-static-site.yml

@@ -13,9 +13,9 @@ jobs:
         uses: actions/setup-node@v2
         with:
           node-version: "16"
-      - name: Check runner state
+      - name: Install yarn
         run: |
-          yarn --version
+          npm install -g yarn
       - name: Install dependencies
         run: yarn install
       - name: Build the static site