ci: fix pnpm version (#10252)

Fixes broken release CI: https://github.com/ethereum-optimism/optimism/actions/runs/8788831115/job/24117187007

We have too many dependencies in the monorepo to manage them all without
accidentally breaking things. We will remove `pnpm` soon TM.

.github/actions/setup/action.yml

@@ -4,9 +4,9 @@ runs:
  using: composite
  steps:
  - name: Setup pnpm
- uses: pnpm/action-setup@v2
+ uses: pnpm/action-setup@v3
  with:
- version: 8.6.5
+ version: 9
  - name: Setup node
  uses: actions/setup-node@v3
  with: