When sites config is migrated, site URLs become hard coded

[duncanmcclean]

Bug description

I've just upgraded a site to v5 and noticed all my site URLs have become hard coded, despite being dynamic via the env() in v4.

If I didn't notice and update the site config, when I deploy to production, the site would break since all my site URLs are .test.

How to reproduce

1. On Statamic 4, setup a multisite, with the URLs for said sites pointing at .env values:

'glasgow' => [
    'name' => 'Harvest Glasgow',
    'locale' => 'en_GB',
    'url' => env('HARVEST_GLASGOW_URL'),
    'attributes' => [
        'launch_year' => 2009,
    ],
],

'ayr' => [
    'name' => 'Harvest Ayr',
    'locale' => 'en_GB',
    'url' => env('HARVEST_AYR_URL'),
    'attributes' => [
        'launch_year' => 2021,
    ],
],

'rooted_conf' => [
    'name' => 'Rooted Conference',
    'locale' => 'en_GB',
    'url' => env('ROOTED_CONF_URL'),
],

'rooted_churches' => [
    'name' => 'Rooted Churches',
    'locale' => 'en_GB',
    'url' => env('ROOTED_CHURCHES_URL'),
],

HARVEST_GLASGOW_URL=https://harvestglasgow.test
HARVEST_AYR_URL=https://harvestayr.test
ROOTED_CONF_URL=https://rootedconf.test
ROOTED_CHURCHES_URL=https://rootedchurches.test

2. Update to Statamic 5
3. See that the upgrade script hard-codes the site URLs:

Logs

No response

Environment

Environment
Application Name: Harvest Statamic
Laravel Version: 10.48.10
PHP Version: 8.3.0
Composer Version: 2.6.3
Environment: local
Debug Mode: ENABLED
URL: harvestglasgow.test
Maintenance Mode: OFF

Cache
Config: NOT CACHED
Events: NOT CACHED
Routes: NOT CACHED
Views: CACHED

Drivers
Broadcasting: log
Cache: redis
Database: mysql
Logs: stack / single
Mail: log
Queue: sync
Session: file

Livewire
Livewire: v3.4.12

Statamic
Addons: 2
Sites: 4 (Harvest Glasgow, Harvest Ayr, Rooted Conference, Rooted Churches)
Stache Watcher: Enabled
Static Caching: Disabled
Version: 5.0.1 PRO

Statamic Addons
duncanmcclean/static-cache-manager: 4.0.0
jonassiewertsen/statamic-livewire: 3.3.0

Installation

Fresh statamic/statamic site via CLI

Additional details

No response