test: update pnpm to v9

README.md

@@ -1,3 +1,7 @@
+> ## :warning: Upgrade from v2!
+>
+> The v2 version of this action [has stopped working](https://github.com/pnpm/action-setup/issues/135) with newer Node.js versions. Please, upgrade to the latest version to fix any issues.
+
 # Setup pnpm
 
 Install pnpm package manager.
@@ -40,7 +44,7 @@ If `run_install` is a YAML string representation of either an object or an array
 
 ### `package_json_file`
 
-**Optional** (_type:_ `string`, _default:_ `package.json`) File path to the `package.json`/[`package.yaml`](https://github.com/pnpm/pnpm/pull/1799) to read "packageManager" configuration.
+**Optional** (_type:_ `string`, _default:_ `package.json`) File path to the `package.json` to read "packageManager" configuration.
 
 ### `standalone`
 

src/install-pnpm/run.ts

@@ -64,7 +64,6 @@ async function readTarget(opts: {
   if (version) {
     if (
       typeof packageManager === 'string' &&
-      packageManager.startsWith('pnpm@') &&
       packageManager.replace('pnpm@', '') !== version
     ) {
       throw new Error(`Multiple versions of pnpm specified: