Fix a bug ast.Merge removes comments from SequenceNode

[suzuki-shunsuke]

• Fix the issue ast.Merge() removes comments in a SequenceNode #569

Before submitting your PR, please confirm the following.

• Describe the purpose for which you created this PR.
• Create test code that corresponds to the modification

[suzuki-shunsuke]

$ go test -covermode=atomic -coverprofile=coverage.txt ./ast
ok  	github.com/goccy/go-yaml/ast	0.202s	coverage: 3.9% of statements

I'm not sure how to add tests.

[suzuki-shunsuke]

CI failed.

https://github.com/goccy/go-yaml/actions/runs/12161271332/job/33915480019?pr=570

debug - 2024-12-04 13:59:06,224 -- Report creating result --- {"result": "RequestResult(error=RequestError(code='HTTP Error 400', params={}, description='{\"message\":\"Token required because branch is protected\"}\\n'), warnings=[], status_code=400, text='{\"message\":\"Token required because branch is protected\"}\\n')"}
error - 2024-12-04 13:59:06,224 -- Report creating failed: {"message":"Token required because branch is protected"}
Error: Codecov:
                        Failed to properly create report: The process '/home/runner/work/_actions/codecov/codecov-action/v4/dist/codecov' failed 

Maybe this is because this is a pull request from a fork repository.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.46%. Comparing base (5d22eed) to head (e6ff4c9).

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #570   +/-   ##
=======================================
  Coverage   77.46%   77.46%           
=======================================
  Files          21       21           
  Lines        7482     7482           
=======================================
  Hits         5796     5796           
  Misses       1291     1291           
  Partials      395      395           

[goccy]

Thank you for your contribution ! LGTM 👍