Fix(Core): fix file upload

[stonebuzz]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

Fix #516

Fix file upload process

Fix this error

[2025-10-02 07:21:23] glpi.CRITICAL:   *** Uncaught PHP Exception Glpi\Exception\Http\HttpException: "Class PluginDatainjectionBackendcsv is not a valid class" at backend.class.php line 84
  Backtrace :
  ./plugins/datainjection/inc/backend.class.php:84   
  ./plugins/datainjection/inc/model.class.php:990    PluginDatainjectionBackend::getInstance()
  ./plugins/datainjection/inc/model.class.php:1047   PluginDatainjectionModel->readUploadedFile()
  ./plugins/datainjection/front/model.form.php:76    PluginDatainjectionModel->processUploadedFile()
  ...Glpi/Controller/LegacyFileLoadController.php:64 require()
  ./vendor/symfony/http-kernel/HttpKernel.php:181    Glpi\Controller\LegacyFileLoadController->__invoke()
  ./vendor/symfony/http-kernel/HttpKernel.php:76     Symfony\Component\HttpKernel\HttpKernel->handleRaw()
  ./vendor/symfony/http-kernel/Kernel.php:197        Symfony\Component\HttpKernel\HttpKernel->handle()
  ./public/index.php:70              

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