chore (v3): properly formatted go.mod and added go.sum

[laverya]

this was done with 'go mod tidy'

[janisz]

What's the status of this? Without go.sum @dependabot is not able to verify dependencies

[msugakov]

This and #539 seem to be the same change. Without either of these merged, github's @dependabot is not able to verify dependencies of our code that depends on go-yaml.
Having go.sum is simply beneficial for reproducible builds and package maintenance tools.
It seems that dependencies of go-yaml have not changed until today so it should be very simple to merge this PR.
Is it possible to merge and release it any time soon @niemeyer?
Thanks!

[SVilgelm]

@niemeyer Could you please look at this? Please update and merge, we really need the go.sum file to properly maintain the dependencies