chore(example): allow using github template without github variables

[R11baka]

Description

Fixed default template related in bug #659

Motivation and Context

How Has This Been Tested?

Screenshots / Logs (if applicable)

Types of Changes

• Bug fix (non-breaking change which fixes an issue)

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.
  How to check ? run in shell
  cargo run --no-default-features -- -c examples/github.toml

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 36.97%. Comparing base (2c2a300) to head (bbace25).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #672      +/-   ##
==========================================
+ Coverage   36.89%   36.97%   +0.08%     
==========================================
  Files          18       18              
  Lines        1350     1350              
==========================================
+ Hits          498      499       +1     
+ Misses        852      851       -1     

Flag	Coverage Δ
unit-tests	36.97% <ø> (+0.08%)	⬆️

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[orhun]

I will accept this as a short term solution, but it does not really fix the actual underlying issue.

git-cliff/git-cliff-core/src/release.rs

Lines 33 to 41 in 2c2a300

	/// Contributors.
	#[cfg(feature = "github")]
	pub github: RemoteReleaseMetadata,
	/// Contributors.
	#[cfg(feature = "gitlab")]
	pub gitlab: RemoteReleaseMetadata,
	/// Contributors.
	#[cfg(feature = "bitbucket")]
	pub bitbucket: RemoteReleaseMetadata,

We should instead have these structs available at all times (even though the feature isn't enabled) so that they are usable in the template although they are empty.

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[R11baka]

@orhun thanks for advice. Will try to implement your solution