fix: remove build restrictions of pyside6 version

[wakonig]

Description

[Provide a brief description of the changes introduced by this pull request.]

Related Issues

[Cite any related issues or feature requests that are addressed or resolved by this pull request. Link the associated issue, for example, with fixes #123 or closes #123.]

Type of Change

• Change 1
• Change 2

How to test

• Run unit tests
• Open [widget] in designer and play around with the properties

Potential side effects

[Describe any potential side effects or risks of merging this PR.]

Screenshots / GIFs (if applicable)

[Include any relevant screenshots or GIFs to showcase the changes made.]

Additional Comments

[Add any additional comments or information that may be helpful for reviewers.]

Definition of Done

• Documentation is up-to-date.

[Copilot]

Pull Request Overview

This PR removes the upper version constraint on PySide6 dependency to allow newer versions beyond 6.9.0. This change enables the package to work with future PySide6 releases while maintaining the minimum required version.

• Removes upper bound restriction on PySide6 version constraint
• Maintains minimum version requirement of 6.8

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}