cli: Fix state migration version check
cli: Fix state migration version check

When migrating multiple local workspaces to a remote backend target
using the `prefix` argument, we need to perform the version check
against all existing workspaces returned by the `Workspaces` method.
Failing to do so will result in a version check error.

tommynsong/terraform,ewbankkit/terraform,tommynsong/terraform,ewbankkit/terraform,ewbankkit/terraform,hashicorp/terraform,rnaveiras/terraform,hashicorp/terraform,ewbankkit/terraform,hashicorp/terraform,rnaveiras/terraform,tommynsong/terraform,rnaveiras/terraform