Migrate skip-author-associations test to canonical YAML import and demote deprecated module

[Copilot]

The repo policy says gopkg.in/yaml.v3 has been migrated to go.yaml.in/yaml/v3, but one workflow test still imported the deprecated path and kept it effectively direct in module metadata. This change aligns the test import and module graph with that policy.

• Import path alignment

  • Updated /pkg/workflow/skip_author_associations_test.go to use the canonical YAML module path.

• Dependency graph cleanup

  • Ran module tidy so gopkg.in/yaml.v3 is no longer a direct requirement in go.mod and is retained only as indirect/transitive where needed.

• Resulting diff shape

  // pkg/workflow/skip_author_associations_test.go
  - "gopkg.in/yaml.v3"
  + "go.yaml.in/yaml/v3"

  # go.mod
  - gopkg.in/yaml.v3 v3.0.1
  + gopkg.in/yaml.v3 v3.0.1 // indirect