Update CI to Go 1.17 - 1.20 (#557)

Update CI to Go 1.17 - 1.20 (#557)

I have no idea if anyone is using Go 1.16 with fsnotify.

Go 1.16 (released August 2021) became mandatory with v1.5.1 (August
2021). Go 1.17 was released just a few days before it was tagged. Some
people did experience problems (#400), but overall the feedback was
limited.

So based on this, I think it's probably safe to just follow the Go
release policy: "Each major Go release is supported until there are two
newer major releases."

This will allow merging #554