Fix composer config and unit tests

[HanXHX]

• Do not add vendor dir in versionning
• Fix autoloading dev
• Add ext-xml dep
• Remove hard dependency to PHP 7.2
• Add PHPUnit dev dep and fix legacy unit tests

[skjnldsv]

Please sign the DCO :)
https://github.com/nextcloud/updater_server/pull/839/checks?check_run_id=11720525838

[nickvergessen]

Remove hard dependency to PHP 7.2

Production still runs it, so blocking for now.

[HanXHX]

Remove hard dependency to PHP 7.2

Production still runs it, so blocking for now.

Did you read the code? => https://github.com/nextcloud-releases/updater_server/pull/839/files#diff-d2ab9925cad7eac58e0ff4cc0d251a937ecf49e4b6bf57f8b95aab76648a9d34L7

With my patch, composer can run on "all" PHP version.

[nickvergessen]

With my patch, composer can run on "all" PHP version.

But anyone updating a dependency might bump it to a version that is not compatible with 7.2 anymore.

[HanXHX]

Please, can you confirm:

• This project must be run only on PHP 7.2 (eol 2020)?
• No plan to support up to date PHP version?
• Is this project supposed to run properly with Nextcloud server with up to date PHP version? (Remember NC26, needs PHP8.0+ => https://docs.nextcloud.com/server/26/admin_manual/installation/system_requirements.html)

[nickvergessen]

• This project must be run only on PHP 7.2 (eol 2020)?
• No plan to support up to date PHP version?

That is not what the platform is about. Please see this documentation page: https://getcomposer.org/doc/06-config.md#platform
Platform specifies a minimum, not an "only version".

• Is this project supposed to run properly with Nextcloud server with up to date PHP version?

This project here runs totally independent and is actually only run by us, not by admins running a Nextcloud Server 26 or whatever other version at home.