fix(parser): allow matching empty commit body

[orhun]

Description

This PR updates the commit parsing to matching empty commit body.

Makes it possible to skip commits with empty body:

[git]
commit_parsers = [
  { body = "$^", skip = true },
]

Motivation and Context

closes #604

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]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 41.41%. Comparing base (adc5c5b) to head (f98278c).
Report is 1 commits behind head on main.

Files	Patch %	Lines
git-cliff-core/src/commit.rs	83.34%	1 Missing ⚠️

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #605      +/-   ##
==========================================
+ Coverage   41.27%   41.41%   +0.14%     
==========================================
  Files          15       15              
  Lines        1071     1070       -1     
==========================================
+ Hits          442      443       +1     
+ Misses        629      627       -2     

Flag	Coverage Δ
unit-tests	41.41% <83.34%> (+0.14%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[bbbenja]

Just tested on my project and it works great, thanks a lot.

[orhun]

Thanks for checking it out!