Pinning nlohmann_json version for xeus-cpp-lite

[anutosh491]

Description

nlohmann_json 3.12.0 was out this week and the current xeus version is only compatible with 3.11.* due to reasons mentioned here

https://github.com/jupyter-xeus/xeus/blob/055829bb0cccd1c5afe904a222c33770d98ef860/CMakeLists.txt#L78-L83

So we have the dependency pinned for our native builds

xeus-cpp/environment-dev.yml

Line 12 in d7699c0

- nlohmann_json=3.11.3

But not for our lite build (So possibly our nightly build should show the error by today/tomorrow when micromamba would pick up 3.12.0 instead of 3.11.3)

I tried the same on my local fork and we would see this error https://github.com/anutosh491/xeus-cpp/actions/runs/14429314765/job/40462192706?pr=8

So pinning it to avoid any errors in the future.

Please tick all options which are relevant.

• Bug fix
• New feature
• Added/removed dependencies
• Required documentation updates

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.56%. Comparing base (d7699c0) to head (b288ad8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #286   +/-   ##
=======================================
  Coverage   80.56%   80.56%           
=======================================
  Files          20       20           
  Lines         957      957           
  Branches       88       88           
=======================================
  Hits          771      771           
  Misses        186      186           

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