We use npm, not yarn in this house

.gitea/workflows/build-and-copy.yaml

@@ -13,9 +13,9 @@ jobs:
         with:
           node-version: 20.x
       - name: Install dependencies 📦
-        run: yarn install --frozen-lockfile
+        run: npm ci
       - name: Build eleventy
-        run: yarn build
+        run: npm run build
         env:
           NODE_ENV: production
           OMNIVORE_API_KEY: ${{ secrets.OMNIVORE_API_KEY }}