config [#50] Workflow에 'vercel login' step 추가

Author: cskime

.github/workflows/pr-preview.yaml

@@ -19,6 +19,8 @@ jobs:
       - uses: actions/checkout@v4
       - name: Install Vercel CLI
         run: npm install --global vercel@latest
+      - name: Login to Vercel
+        run: vercel login --token=${{ secrets.VERCEL_TOKEN }}
       - name: Get Vercel Environment Variables
         run: vercel pull --yes --environment=preview --token=${{ secrets.VERCEL_TOKEN }}
       - name: Build Project Artifacts