[drone] multiple anchor references fail

[jimsheldon]

Steps to reproduce

1. Create example.yml

   kind: pipeline
   type: docker
   name: default
   
   anchors:
    - &first_anchor
      FIRST_VAR: value
    - &second_anchor
      SECOND_VAR: value
   
   steps:
    - name: hello
      image: busybox
      environment:
        <<: *first_anchor
        <<: *second_anchor
      commands:
      - echo hello
   
   trigger:
    branch:
    - main

2. Run go-convert

   go-convert drone example.yml
   2023/03/13 16:50:27 yaml: unmarshal errors:
    line 16: mapping key "<<" already defined at line 15

[bradrydzewski]

go-convert is using the latest version of go-yaml. runner-go (drone) may be using a fork from buildkite. we should be able to use just the buildkite fork in the drone package, but still use go-yaml for everything else. cc @eoinmcafee00 can you take a look?

[eoinmcafee00]

PR raised for this issue: https://github.com/drone/go-convert/pull/13 @bradrydzewski