fix: install pnpm before building libvirt

Author: elibosley

.github/workflows/build-libvirt.yml

@@ -29,13 +29,20 @@ jobs:
       with:
         python-version: '3.10'
 
+
     - name: Set Node.js
       uses: actions/setup-node@v4
       with:
         node-version: 20.x
         cache: 'pnpm'
         cache-dependency-path: './libvirt/pnpm-lock.yaml'
 
+    - uses: pnpm/action-setup@v4
+      name: Install pnpm
+      with:
+        version: 8
+        run_install: false
+
     - name: Cache APT Packages
       uses: awalsh128/cache-apt-pkgs-action@v1.4.3
       with: