feat: update go directive to 1.20

[mauri870]

The github.com/klauspost/compress recently deprecated go 1.19 and moved to a go 1.20 directive in go.mod

[mauri870]

Wondering why we don't move to a supported go version, such as 1.21 and 1.22?

[dnwe]

@mauri870 thanks for the PR — a bump to 1.20 is fine to allow us to keep pulling in compress updates. We don't tend to bump the go directive in go.mod further than that until we (or one of our direct dependencies) is using some newer part of the Go language that requires a newer toolchain in order to compile. Whilst Go themselves officially only maintain support for the latest N and N-1 versions, there will be various people using Sarama from Debian stable / Ubuntu LTS / RedHat Enterprise etc. and potentially using the Go toolchain supplied and maintained by the vendor with backported security patches etc.