Symfony version(s) affected

6.4.0

Description

My project uses the asset mapper and as here described:
https://symfony.com/doc/current/frontend/asset_mapper.html#importing-3rd-party-javascript-packages
i downloaded bootstrap with the --download option (which is not working either in 6.4. - documentation issue too).
This generates
'downloaded_to' => 'vendor/....'
Entries in importmap.php which then cause a exception when calling {{ importmap() }} in twig or when trying to update importmaps.
Deleting these downloaded_to fixes the problem after running
bin/console importmap:update

How to reproduce

Install symfony 6.3, add assetmapper, run
php bin/console importmap:require bootstrap --download
Upgrade to symfony 6.4 (including recipes updates)
run bin/console importmap:update
It gives a error:
`In ImportMapConfigReader.php line 46:

The following keys are not valid for the importmap entry "bootstrap": "downloaded_to". Valid keys are: "path", "version", "type", "entrypoint", "url", "package_specifier".
`

Possible Solution

flex recipes should sanatize importmap.php or the importmap:update should handle the upgrade situation

Additional Context

No response