Galette

PHP 8-rc1 has been released, some changes may be required in Galette for compatibility.

Main problem is probably not Galette itself; but some dependencies:
- faker: stucked on an old version already patched for php 7.4, upgrading would require to rewrite many unit tests,
- laminas-db: beacause of on old bug on the lib (see #1299)
- pimple: dependency injection no longer maintained; and not compatible with other alternatives... Switching to php-di would be required; I do not see any other solution
- atoum: a php8 patch has been proposed upstream, see https://github.com/atoum/atoum/pull/843

This is an non exhaustive list.