ci: fix pnpm action version

Author: yyx990803

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       - uses: actions/checkout@v3
 
       - name: Install pnpm
-        uses: pnpm/action-setup@v3
+        uses: pnpm/action-setup@v2
 
       - name: Set node version to 16
         uses: actions/setup-node@v3