Update deploy-preview.yml

Author: sserrata

.github/workflows/deploy-preview.yml

@@ -164,6 +164,7 @@ jobs:
         uses: FirebaseExtended/action-hosting-deploy@0cbcac4740c2bfb00d632f0b863b57713124eb5a # v0.9.0
         with:
           repoToken: "${{ secrets.GITHUB_TOKEN }}"
+          firebaseServiceAccount: "${{ env.SERVICE_ACCOUNT_KEY }}"
           projectId: pandev
           expires: 30d
           channelId: "pr${{ github.event.number }}"