Fix allocation value not updating on switching selected tyre.

[nutzboi]

Fix allocation value spinner not updating on switching selected tyre type in server configuration dialog.

Agreement

By creating a pull request in stk-code, you hereby agree to dual-license your contribution as
GNU General Public License version 3 or any later version and
Mozilla Public License version 2 or any later version.

This includes your previous contribution(s) under the same name of contributor.

Keep the above statement in the pull request comment for agreement.

[Nomagno]

Thanks! uhhh github's 'change base branch' feature is a bit confused but it got the spirit. I'll cherry-pick the commit. Please open PRs to tyre2X-dev instead in the future

[nutzboi]

ah i didn't notice gh picked the default branch ,sry 🥸.