fix(template): include for-loop arguments in template variables

[orhun]

Description

Tobias Bieniek on Mastodon reported that even when he used the GitHub-related template variables in this comment, git-cliff wasn't querying GitHub.

The problem turned out to be in the AST parsing. It was simply not taking for-loop arguments into account.

Motivation and Context

Fixes the issue that mentioned above.

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

All modified and coverable lines are covered by tests ✅

Project coverage is 39.75%. Comparing base (3b6156d) to head (2241703).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #812      +/-   ##
==========================================
+ Coverage   39.50%   39.75%   +0.25%     
==========================================
  Files          20       20              
  Lines        1633     1638       +5     
==========================================
+ Hits          645      651       +6     
+ Misses        988      987       -1     

Flag	Coverage Δ
unit-tests	39.75% <100.00%> (+0.25%)	⬆️

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