Bump etcd to 3.4

[errordeveloper]

This version is latest commit on release-3.4, but go mod picks up and odd tag prefix for it (probably because package is not v3, so it looks for a v0 tag for whatever reason).

[CLAassistant]

All committers have signed the CLA.

[errordeveloper]

I'm updating this so that project where gocsi is vendored can move to a more recent version of etcd and grpc.