fix(changelog): allow using --bumped-version without conventional commits

[orhun]

Motivation and Context

fixes #805

How Has This Been Tested?

Locally.

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 (no code change)
• Refactor (refactoring production code)
• Other

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• I have formatted the code with rustfmt.
• I checked the lints with clippy.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 50.00000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 39.71%. Comparing base (a71649b) to head (527d772).

Files	Patch %	Lines
git-cliff-core/src/config.rs	57.15%	3 Missing ⚠️
git-cliff/src/lib.rs	0.00%	2 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #806      +/-   ##
==========================================
+ Coverage   39.61%   39.71%   +0.10%     
==========================================
  Files          20       20              
  Lines        1606     1607       +1     
==========================================
+ Hits          636      638       +2     
+ Misses        970      969       -1     

Flag	Coverage Δ
unit-tests	39.71% <50.00%> (+0.10%)	⬆️

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