docs: remove v2 warning

@zkochan If you have tested that it work with newer Node.js versions, this warning can be removed.

README.md

@@ -1,7 +1,3 @@
-> ## :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.
@@ -80,7 +76,7 @@ jobs:
     steps:
       - uses: pnpm/action-setup@v4
         with:
-          version: 9
+          version: 8
 ```
 
 ###  Install only pnpm with `packageManager`
@@ -116,7 +112,7 @@ jobs:
 
       - uses: pnpm/action-setup@v4
         with:
-          version: 9
+          version: 8
           run_install: |
             - recursive: true
               args: [--frozen-lockfile, --strict-peer-dependencies]
@@ -141,7 +137,7 @@ jobs:
       - uses: pnpm/action-setup@v4
         name: Install pnpm
         with:
-          version: 9
+          version: 8
           run_install: false
 
       - name: Install Node.js

src/install-pnpm/run.ts

@@ -5,7 +5,6 @@ import { readFileSync } from 'fs'
 import path from 'path'
 import { execPath } from 'process'
 import util from 'util'
-import * as yaml from 'yaml'
 import { Inputs } from '../inputs'
 
 export async function runSelfInstaller(inputs: Inputs): Promise<number> {
@@ -79,18 +78,10 @@ Otherwise, please specify the pnpm version in the action configuration.`)
   }
 
   if (typeof packageManager !== 'string') {
-    if (GITHUB_WORKSPACE) {
+    throw new Error(`No pnpm version is specified.
-      try {
-        const { lockfileVersion } = yaml.parse(readFileSync(path.join(GITHUB_WORKSPACE, 'pnpm-lock.yaml'), 'utf8'))
-        const version = getPnpmVersionFromLockfile(lockfileVersion);
-        return `${ standalone ? '@pnpm/exe' : 'pnpm' }@${version}`
-      } catch (error: unknown) {
-        throw new 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"`)
-      }
-    }
   }
 
   if (!packageManager.startsWith('pnpm@')) {
@@ -104,21 +95,4 @@ Please specify it by one of the following ways:
   return packageManager
 }
 
-function getPnpmVersionFromLockfile(
-  lockfileVersion: string | undefined
-): string | undefined {
-  switch (true) {
-    case lockfileVersion === '5.3':
-      return 'latest-6';
-    case lockfileVersion === '5.4':
-      return 'latest-7';
-    case lockfileVersion === '6.0' || lockfileVersion === '6.1':
-      return 'latest-8';
-    case lockfileVersion === '7.0' || lockfileVersion === '9.0':
-      return 'latest-9';
-    default:
-      return undefined;
-  }
-}
-
 export default runSelfInstaller