Fix API Version for OCI Repository in Flux deployment tutorial

What does this MR do and why?

Ths fixes the used API Version for the OCI repository in the docs.

OCIRepository only available in v1beta2, as can be seen here:

• https://fluxcd.io/flux/components/source/api/v1/
• https://fluxcd.io/flux/components/source/api/v1beta2/