chore: Upgrade yaml v3

[lukemassa]

what

Upgrade gopkg.in/yaml from v2 to v3.

why

Keeping dependencies up to date.

This was built off of a failing renovate run. There are two issues to deal with upgrading from v2 to v3.

1. UnmarshalStrict is no longer available (Support for Unmarshalling strict in yaml v3 go-yaml/yaml#602). You have to use Decode() with KnownFields set to true. Decode has slightly different semantics to Unmarshal (Reading empty file causes Decode to return error go-yaml/yaml#805), so I wrapped these calls in the unit tests. In the actual code I just write the full implementation out so it's more clear, but that would have been quite a bit of copy/paste for unit tests.
2. There's a bug in yaml v3 where it doesn't parse empty elements in arrays properly (Reading empty file causes Decode to return error go-yaml/yaml#805). We were only doing this in unit tests, so I had to in a few places replace - with - {}.

tests

Unit tests

references

Obsoletes: #3974