fix(tag): show source file in unformatted error message

[curbengh]

What does it do?

Error caused by the following example is not formatted by formatNunjucksError() (because err.message doesn't contain Line x, Column y), so the error message still shows (unknown path) which is not helpful. This PR replace it with source path.

{% test %}
${#var}
{% endtest %}

Screenshots

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.

[github-actions]

How to test

git clone -b template-error-source https://github.com/curbengh/hexo.git
cd hexo
npm install
npm test

[coveralls]

Coverage decreased (-0.03%) to 98.009% when pulling fd882ab on curbengh:template-error-source into bbf09ac on hexojs:master.