Add test fixtures for `GIT_CLIFF_INCLUDE_PATH` multiple-value handling

[ognis1205]

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Feature description

We fixed the behavior of GIT_CLIFF_INCLUDE_PATH and --include-path (GIT_CLIFF_EXCLUDE_PATH and --exclude-path as well) to correctly handle multiple glob patterns (space-separated and repeated flags), but we currently lack test fixtures that cover all these cases.

This issue tracks adding test fixtures to ensure that all three usage patterns produce the same result and remain stable over time.

Desired solution

The following three approaches should produce identical changelog output:

1. Environment variable with space-separated globs:

export GIT_CLIFF_INCLUDE_PATH="website/**/* .github/**/*"
git cliff

2. Single --include-path argument with space-separated globs:

git cliff --include-path 'website/**/* .github/**/*'

3. Multiple --include-path arguments:

git cliff --include-path 'website/**/*' --include-path '.github/**/*'

Alternatives considered

N/A

Additional context

#123 (comment)