The Kubernetes provider wanted to return Unimplemented for both
DiffConfig and CheckConfig. However, due to an interaction between the
package we used to construct the error we are returning and the
package we are using to actually construct the gRPC server for the
provider, we ended up in a place where the provider would actually end
up returning an error with code "Unknown", and the /text/ of the
message included information about it being due to the RPC not being
implemented.
So, when we try to call Diff/Check config on the provider, detect this
case as well and treat messages of this shape as if the provider just
returned "Unimplemented".
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