ci(workflows): migrate setup bootstrap to pnpm/setup@v1

[stipsan]

Summary

• Migrate the reusable format and changesets workflows from the split pnpm/action-setup + actions/setup-node bootstrap to a single pnpm/setup@v1 step, porting the pattern from sanity-io/sanity#13233.
• format.yml: uses pnpm/setup@v1 with cache: true and runtime: node@lts. Drops the explicit pnpm install step since pnpm/setup@v1 installs by default.
• changesets.yml: uses pnpm/setup@v1 with install: false, cache: true, and runtime: node@22. Keeps the explicit pnpm install step to preserve the OIDC npm-upgrade ordering and the Node 22 pin.

Notes

• runtime uses pnpm's packageManager syntax, so lts/* became lts.
• Pin comment and OIDC comment lightly updated to drop references to the removed setup-node.
• No remaining pnpm/action-setup / actions/setup-node references in the repo.

Test plan

• CI runs the reusable workflows successfully via downstream consumers
• pnpm store caching works as expected

Made with Cursor