Add unit tests for DNS Policy resource

[Ruhika1417]

What problem are you facing?

Currently, there are no unit tests for the DNS Policy Resource.

How could Crossplane help solve your problem?

It would be nice to have unit tests written for the newly implemented DNS Policy Resource, just like we have them for other resources.

Do see:

https://github.com/crossplane-contrib/provider-gcp/tree/master/pkg/controller/dns https://github.com/crossplane-contrib/provider-gcp/tree/master/pkg/clients/dns