Fix DotEnv dependency

Summary:
Recent DotEnv versions are built through DotEnv::createImmutable.

To prevent further changes (if any) to break the installation,
pin the current PHP 8.2 compatible version to composer.

Test Plan: Browse wiki, the environment variables are correctly read

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D3050