chore: remove strong upper bound on build dep

[SMoraisAnsys]

Description

Following #544, the upper bound on flit_core shouldn't be needed anymore.

Issue linked

None

Checklist

• I have tested my changes locally.
• I have added necessary documentation or updated existing documentation.
• I have followed the coding style guidelines of this project.
• I have added appropriate tests (unit, integration, system).
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved by the PR if any.
• I have assigned this PR to myself.
• I have made sure that the title of my PR follows Conventional commits style (e.g. feat: add optical property)
• I have agreed with the Contributor License Agreement (CLA).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.42%. Comparing base (904f6c4) to head (282c0a5).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #549   +/-   ##
=======================================
  Coverage   87.42%   87.42%           
=======================================
  Files          37       37           
  Lines        3943     3943           
=======================================
  Hits         3447     3447           
  Misses        496      496           

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