Hello @Kopl ,
Welcome to Microsoft QnA.
Apologies for the delay in response. The reason why you haven't yet received any responses on this thread is because GitHub Actions is as of now not supported on Microsoft QnA Platform.
However, after doing some research, here is something relevant that I have found which might be the cause behind this error. Please check the below.
Starting with 1.23 AKS will follow upstream kubernetes and deprecate in-tree azure authentication which is marked for deprecation to be replaced with 'exec'. If you are using Azure CLI or Azure clients, AKS will download kubelogin for users automatically. If outside of Azure CLI, users need to download and install kubelogin in order to continue to use kubectl with AAD authentication
Please go through #2728 and reference release 2022-05-22 for more details.
Do let me know if this helps?