[FEATURE] Update to Go 1.21

[SaschaSchwarze0]

Is there an existing feature request for this?

• I have searched the existing feature requests

Is your feature request related to a problem or use-case? Please describe.

Go 1.20 is end of support already.

Describe the solution that you would like.

We should update go.mod and CI to use Go 1.21. PR should be similar to the last one

Describe alternatives you have considered.

No response

Anything else?

No response