ci: pin pnpm to v9 for Node 20 workflows

Author: lius

.github/workflows/ci.yml

@@ -38,10 +38,10 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Setup pnpm
-        uses: pnpm/action-setup@v4
-        with:
-          version: latest
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          version: 9
 
       - name: Setup Node.js
         uses: actions/setup-node@v4

.github/workflows/tauri-build-win.yml

@@ -57,7 +57,7 @@ jobs:
       - name: Setup pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: latest
+          version: 9
 
       - name: Setup Node.js
         uses: actions/setup-node@v4