Fix build.yml workflow

[abelsiqueira]

Checklist before requesting a review

• I have read the contribution guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• All user facing changes have been added to CHANGELOG.md

Type of change

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

List of related issues or pull requests**

Refs:

• Invalid workflow file .github/workflows/build.yml #636

Describe the changes made in this pull request

The build.yml was broken because it was not being processed by Jinja. Adding the .jinja extension fixed that.
Then it was broken because whitespace stripping was concatenating the lint from AddLinting.

Instructions to review the pull request

Suggestions for review:

• Copy and check .github/workflows/build.yml
• Copy, create a repo, push, and see the build workflow. It has errors, but the file itself is correct now. Here is an example: https://github.com/abelsiqueira/mypkg18/actions/runs/10621564752/job/29443810955

Install the requirements

cd $(mktemp -d --tmpdir py-tmpl-XXXXXX)
pip install pipx
pipx install copier

Create a new package using the template

copier copy --vcs-ref <YOUR_BRANCH> https://github.com/nlesc/python-template test_package

Create a local git repo to push to GitHub to trigger CI actions

git init
git add --all
git commit -m "First commit"
git remote add origin git@github.com:<YOU>/python-template-test.git
git push -u origin main -f

[fdiblen]

Works as expected. Thank you, @abelsiqueira