Repository: create-react-app
Issue: In CRA 5.0.0, `react-scripts start` fails when both `HOST` in `.env` and `proxy` in `package.json` are defined.
Labels: issue: bug,needs triage,issue: bug report

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### Describe the bug

In CRA 5.0.0, `react-scripts start` fails when both `HOST` in `.env` and `proxy` in `package.json` are defined.

### Did you try recovering your dependencies?

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This occurs on a newly created project.

### Which terms did you search for in User Guide?

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"allowedHosts" and others, came up empty.

### Environment

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```
Environment Info:

  current version of create-react-app: 5.0.0
  running from /home/z003w3we/.npm/_npx/c67e74de0542c87c/node_modules/create-react-app

  System:
    OS: Linux 5.4 Ubuntu 20.04.3 LTS (Focal Fossa)
    CPU: (4) x64 Intel(R) Core(TM) i7-9850H CPU @ 2.60GHz
  Binaries:
    Node: 16.13.0 - ~/.asdf/installs/nodejs/16.13.0/bin/node
    Yarn: 1.22.10 - ~/.asdf/shims/yarn
    npm: 8.1.3 - ~/.asdf/plugins/nodejs/shims/npm
  Browsers:
    Chrome: 96.0.4664.45
    Firefox: 95.0
  npmPackages:
    react: ^17.0.2 => 17.0.2 
    react-dom: ^17.0.2 => 17.0.2 
    react-scripts: 5.0.0 => 5.0.0 
  npmGlobalPackages:
    create-react-app: Not Found
```

### Steps to reproduce

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1. Create a new app.
2. Set `HOST` in `.env`.
3. Set `proxy` in `package.json`.
4. Run `react-scripts start` or something to that effect.

### Expected behavior

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App starts.

### Actual behavior

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I get this error:

```
> yarn start
yarn run v1.22.10
$ react-scripts start
Attempting to bind to HOST environment variable: test.localhost
If this was unintentional, check that you haven't mistakenly set it in your shell.
Learn more here: https://cra.link/advanced-config

Invalid options object. Dev Server has been initialized using an options object that does not match the API schema.
 - options.allowedHosts[0] should be a non-empty string.
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
```

### Reproducible demo

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https://github.com/BalzGuenat/cra-test

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