manifest.json generated with wrong filename

Manifest Plugin Version: 3.0.0
Webpack Version: 5.21.2
Operating System (or Browser): macOS Big Sur
Node Version: v15.7.0
Link to reproduction: https://codesandbox.io/s/loving-archimedes-sgp20?file=/static/frontend/manifest.json

Webpack config:
```
const path = require('path');
```

const { WebpackManifestPlugin } = require('webpack-manifest-plugin'); const { CleanWebpackPlugin } = require('clean-webpack-plugin');

module.exports = { context: path.resolve(__dirname, 'src'), entry: ['./index.tsx'], mode: 'development', module: { rules: [ { exclude: /node_modules/, test: /.(ts|tsx)?$/, use: ['babel-loader', 'ts-loader'], }, ], }, plugins: [new CleanWebpackPlugin(), new WebpackManifestPlugin()], resolve: { extensions: ['.ts', '.tsx', '.js'], }, output: { path: path.resolve(__dirname, 'static/frontend/'), filename: '[name].[hash].js', }, };



### Expected Behavior
`{
  "main.js": "main.6b7fd6ac2fd4fec33833.js"
}`

### Actual Behavior
`{
  "main.js": "automain.6b7fd6ac2fd4fec33833.js"
}`

Weird "auto" prefix in filename as `publicPath`.

shellscape / webpack-manifest-plugin

manifest.json generated with wrong filename #250