Blueprint defaults with `pnpm` result in broken CI initially

[runspired]

Run pnpm/action-setup@v4
Running self-installer...
  Error: No pnpm version is specified.
  Please specify it by one of the following ways:
    - in the GitHub Action config with the key "version"
    - in the package.json with the key "packageManager"
      at readTarget (/home/runner/work/_actions/pnpm/action-setup/v4/dist/index.js:1:5635)
      at runSelfInstaller (/home/runner/work/_actions/pnpm/action-setup/v4/dist/index.js:1:4142)
      at async install (/home/runner/work/_actions/pnpm/action-setup/v4/dist/index.js:1:3154)
      at async main (/home/runner/work/_actions/pnpm/action-setup/v4/dist/index.js:1:445)
  Error: Error: No pnpm version is specified.
  Please specify it by one of the following ways:
    - in the GitHub Action config with the key "version"
    - in the package.json with the key "packageManager"

There's a number of ways we could add this, using packageManager is probably the most universal.