fix: setting tokens as burnable when migrating handlers

[nmlinaric]

Description

When migrating to new ERC20 handlers script didn't set burnable tokens as burnable on new ERC20 handler.

Related Issue Or Context

How Has This Been Tested? Testing details.

manual tests

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation

Checklist:

• I have commented my code, particularly in hard-to-understand areas.
• I have ensured that all acceptance criteria (or expected behavior) from issue are met
• I have updated the documentation locally and in chainbridge-docs.
• I have added tests to cover my changes.
• I have ensured that all the checks are passing and green, I've signed the CLA bot