fix(core): keep modern writer template when preset ships a legacy writer guard - #4415

Description

normalizeLegacyWriterOptions compiles any string writer.mainTemplate it finds and assigns the result to writer.template. Presets built on @conventional-changelog/template ship such a string on purpose: it is a guard that renders to a "you need conventional-changelog-writer@9 or newer" error, and it sits next to the real function-based template. Since the guard is only meant to be read by an old writer, normalizing it throws away the working template and makes the bundled v9 writer render the error instead.

The normalization now leaves the writer options alone when writer.template is already a function.

Motivation and Context

lerna version --conventional-commits with conventional-changelog-conventionalcommits@10.4.0 fails with:

Missing helper: "conventional-changelog-conventionalcommits requires conventional-changelog-writer@9 or newer (conventional-changelog@8 or newer). Your changelog tooling loaded an older writer which cannot render this preset. Update the tooling or use an older major version of the preset."

Fixes #4414

How Has This Been Tested?

Added a unit test with a fixture preset that carries both a guard mainTemplate and a modern template. It reproduces the error on main and passes here. Also ran nx test core, nx test commands-version, nx test commands-publish, lint and format:check.

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)
• Chore (change that has absolutely no effect on users)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.