ci: update pnpm to v8

Author: haoqunjiang

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
       - name: Install pnpm
         uses: pnpm/action-setup@v2
         with:
-          version: 7
+          version: 8
 
       - name: Set node version to 16
         uses: actions/setup-node@v2