chore: disable hardfork proposal test

[kneerose]

List of changes

• Add env flag for hardfork propsoal test
• Disable hardfork proposal test if IS_HARDFORK_PROPOSAL_ENABLED env is set to false and not provided

Checklist

• related issue
• My changes generate no new warnings
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the changelog
• I have added tests that prove my fix is effective or that my feature works

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[github-actions]

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