[Bug] `devEngines.packageManager` set to pnpm in `package.json` prevents local-action from running `npm exec tsx`

I'm using `pnpm` as the package manager. However, with the following `package.json` settings, local-action failed to start when running `pnpm run local-action`.

```json
{
"name": "github-action",
"version": "1.0.0",
"description": "",
"keywords": [],
"license": "MIT",
"author": "",
"type": "module",
"scripts": {
"local-action": "local-action . src/main.ts .env",
},
"devDependencies": {
"@github/local-action": "^7.0.1"
},
"devEngines": {
"packageManager": {
"name": "pnpm",
"version": "^11.5.2",
"onFail": "download"
}
}
}
```

Below is the error log:

```
npm error code EBADDEVENGINES
npm error EBADDEVENGINES The developer of this package has specified the following through devEngines
npm error EBADDEVENGINES Invalid devEngines.packageManager
npm error EBADDEVENGINES Invalid name "pnpm" does not match "npm" for "packageManager"
npm error EBADDEVENGINES {
npm error EBADDEVENGINES current: { name: 'npm', version: '11.13.0' },
npm error EBADDEVENGINES required: { name: 'pnpm', version: '^11.5.2', onFail: 'download' }
npm error EBADDEVENGINES }
npm error A complete log of this run can be found in: //.npm/_logs/2026-06-11T14_13_09_439Z-debug-0.log

Error: Command failed: npm exec tsx "/node_modules/.pnpm/@github+local-action@7.0.1/node_modules/@github/local-action/src/index.ts" -- . src/main.ts .env
at genericNodeError (node:internal/errors:985:15)
at wrappedFn (node:internal/errors:539:14)
at checkExecSyncError (node:child_process:925:11)
at execSync (node:child_process:997:15)
at entrypoint (file:///node_modules/.pnpm/@github+local-action@7.0.1/node_modules/@github/local-action/bin/local-action.js:108:5)
at file:///node_modules/.pnpm/@github+local-action@7.0.1/node_modules/@github/local-action/bin/local-action.js:121:1
at ModuleJob.run (node:internal/modules/esm/module_job:439:25)
at async onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:633:26)
at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:101:5) {
status: 1,
signal: null,
output: [ null, null, null ],
pid: 70918,
stdout: null,
stderr: null
}
[ELIFECYCLE] Command failed with exit code 1.
```

It seems that setting `devEngines.packageManager` set to pnpm in `package.json` prevents local-action from running `npm exec tsx "/node_modules/.pnpm/@github+local-action@7.0.1/node_modules/@github/local-action/src/index.ts" -- . src/main.ts .env`.

Consider running `tsx` without relying on package manager by adding `tsx` as dependency. This makes local-action independent from package managers.

Start with the package.json reproduction and the local-action command, then inspect the local-action.js entry point shown in the stack trace around the npm exec invocation. Reproduce the failure with pnpm and devEngines.packageManager set to pnpm; done means pnpm run local-action starts successfully without the EBADDEVENGINES error.

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