Prefer British spelling for issue template. - #11

Description

A small change of language to prefer British spelling of Behaviour over the American spelling.

Change Log

• Change Behavior for Behaviour.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• I have disclosed all areas where AI assistance was used when creating this pull request, if applicable
• AI code suggestions have been manually reviewed and I understand how they work