Update CHANGELOG.md for release v0.12.6

[vearutop]

🤔 What's changed?

CHANGELOG is prepared for a new release.

⚡️ What's your motivation?

We haven't released a new version for a while and we have some helpful changes in main.

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, documentation etc. without changing behaviour)

♻️ Anything particular you want feedback on?

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

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[github-actions]

Go API Changes

# github.com/cucumber/godog
## compatible changes
Feature: added

# summary
Inferred base version: v0.12.5
Suggested version: v0.13.0