ci: bump pnpm/update to run self-update before the dependency update (#13516)

Picks up pnpm/update#4: the pin bump now happens first, so the
dependency update and the refreshed lockfile are produced by the pnpm
version the update PR moves the repository onto.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/update-lockfile.yml

@@ -44,7 +44,7 @@ jobs:
         install: false
 
     - name: Update dependencies, Node.js, pnpm, and GitHub Actions
-      uses: pnpm/update@9a256174a439f3447aa0a6b9ca3c971428b1d617 #v0.0.0  v0
+      uses: pnpm/update@fcaa952ef94bad62067a94ac2e5c6234b648e259 #v0.0.0  v0
       with:
         update-deps: latest
         refresh-lockfile: true