Fixed validate function import

[tomast1337]

This pull request includes changes to the server/src/app.module.ts file to update the import path for the validate function and simplify its usage.

Improvements to import paths and usage:

• Updated the import path for the validate function to use ./config/EnvironmentVariables instead of class-validator.
• Simplified the usage of the validate function by removing the redundant assignment in the ConfigModule.forRoot method.