Fix make gen and rerun it.

[jkh52]

Vendoring the top level module broke make gen: #558.

$ make gen
go mod download
protoc -I . konnectivity-client/proto/client/client.proto --go_out=. --go_opt=paths=source_relative --go-grpc_out=require_unimplemented_servers=false:. --go-grpc_opt=paths=source_relative
cat hack/go-license-header.txt konnectivity-client/proto/client/client_grpc.pb.go > konnectivity-client/proto/client/client_grpc.licensed.go
mv konnectivity-client/proto/client/client_grpc.licensed.go konnectivity-client/proto/client/client_grpc.pb.go
protoc -I . proto/agent/agent.proto --go_out=. --go_opt=paths=source_relative --go-grpc_out=require_unimplemented_servers=false:. --go-grpc_opt=paths=source_relative
cat hack/go-license-header.txt proto/agent/agent_grpc.pb.go > proto/agent/agent_grpc.licensed.go
mv proto/agent/agent_grpc.licensed.go proto/agent/agent_grpc.pb.go
mkdir -p proto/agent/mocks
mockgen sigs.k8s.io/apiserver-network-proxy/proto/agent AgentService_ConnectServer > proto/agent/mocks/agent_mock.go
prog.go:13:2: cannot find module providing package go.uber.org/mock/mockgen/model: import lookup disabled by -mod=vendor
        (Go version in go.mod is at least 1.14 and vendor directory exists.)
prog.go:13:2: cannot find module providing package go.uber.org/mock/mockgen/model: import lookup disabled by -mod=vendor
        (Go version in go.mod is at least 1.14 and vendor directory exists.)
prog.go:13:2: no required module provides package go.uber.org/mock/mockgen/model: go.mod file not found in current directory or any parent directory; see 'go help modules'
prog.go:15:2: no required module provides package sigs.k8s.io/apiserver-network-proxy/proto/agent: go.mod file not found in current directory or any parent directory; see 'go help modules'
2024/02/16 14:31:24 Loading input failed: exit status 1
make: *** [Makefile:54: mock_gen] Error 1```

[jkh52]

/assign @cheftako

[cheftako]

/lgtm
/approve

[k8s-ci-robot]

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