Update to go 1.16.x

What does this MR do?

Updates the used Go version to 1.16.x

This is a successor of !2710 (closed).

Why was this MR needed?

We're currently on 1.13.8, while the recent stable version of Go is 1.16.x. We're - AGAIN - on an unsupported version of Go.

Since we're not blocked (or rather - we don't know about any blocker) from bumping the version up, as we were with Go 1.8, let's just do this. And see if all is OK 🙂

What's the best way to test this MR?

What are the relevant issue numbers?

Closes #27568 (closed)