chore: specify packageManager version in package.json

Following the instructions in
https://vercel.com/docs/errors/error-list#pnpm-engine-unsupported

It should fix the error:

```text
Using package.json#engines.pnpm without corepack and package.json#packageManager could lead to failed builds with ERR_PNPM_UNSUPPORTED_ENGINE. Learn more: https://vercel.com/docs/errors/error-list#pnpm-engine-unsupported
 ERR_PNPM_UNSUPPORTED_ENGINE  Unsupported environment (bad pnpm and/or Node.js version)
```
```

package.json

@@ -34,6 +34,7 @@
     "node": "^18.0.0 || >=20.0.0",
     "pnpm": ">=8 <9"
   },
+  "packageManager": "[email protected]",
   "devDependencies": {
     "@changesets/changelog-github": "0.5.0",
     "@changesets/cli": "2.27.7",