Disable grpc_cli tests

Description

Google recently moved the location of the protobuf repository from https://github.com/google/protobuf.git to https://github.com/protocolbuffers/protobuf.git. This had the side effect of breaking the gRPC CMake build, because the submodule URL was pointing to the wrong place. A fix is in progress for this, but it will not propagate to older gRPC versions, so this e2e test is broken as is.

Disable e2e tests related to grpc_cli. In the future, we can re-enable these with an updated RELEASE_TAG once a version with the correct submodule location is released.