fix: correct type of verson in CustomAdaptiveCard

[tinect]

Version must be a string otherwise, M$ will answer with an exception.
Additionally, the new workflow will result with empty string instead of "1".

[sebbmeyer]

Thanks @tinect for the PR, it will try to review it as soon as I can

[janmyszkier]

@sebbmeyer I can confirm this is needed and PR is correct. Eventually might be a good idea to change all versions around the code to strings like it's done in https://github.com/sebbmeyer/php-microsoft-teams-connector/blob/master/src/Cards/Adaptive/BaseAdaptiveCard.php#L23

[sebbmeyer]

@janmyszkier thanks for checking the PR. I try check every open PR on the weekend and merge it