cache pnpm and runtime when `cache` is enabled

[SuperchupuDev]

the following installs node & pnpm every time it's ran, as they do not get cached (they get downloaded & installed before cache is recovered)

uses: pnpm/setup@v2.1.0
  with:
  runtime: node@26
  cache: true

Run pnpm/setup@v2
# no cache here
Installing pnpm...
Installation Completed!
Installing runtime node@26...
Restoring cache...
# there is cache now

ref: https://github.com/SuperchupuDev/tinyglobby/actions/runs/33325776540/job/99295515418