chore: bump back down to pnpm 9

Co-authored-by: graphite-app[bot] <96075541+graphite-app[bot]@users.noreply.github.com>

Author: billyb2

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
       - name: Install pnpm
         uses: pnpm/action-setup@v4.0.0
         with:
-          version: 10.x.x
+          version: 9.x.x
 
       - name: Install Node 24
         uses: actions/setup-node@v4