Add the upload artifact action

[paulbalandan]

Description
Docs action still fails because it cannot cp the user guide folder. This adds the actions/upload-artifact. This is also referenced in ammaraskar/sphinx-action-test default workflow.

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[lonnieezell]

Awesome, thanks. I hadn't had a chance to get back to it yet.

[samsonasik]

The docs_nightly docs github action seems still failure in latest develop at https://github.com/codeigniter4/CodeIgniter4/runs/836152216

Run actions/upload-artifact@v2

##[warning]No files were found for the provided path: user_guide_src/_build/html/. No artifacts will be uploaded.
Run actions/upload-artifact@v2
##[warning]No files were found for the provided path: user_guide_src/_build/html/. No artifacts will be uploaded.
Commit documentation changes

##[error]Process completed with exit code 1.
Run git clone https://github.com/codeigniter4/CodeIgniter4.git --branch gh-pages --single-branch gh-pages
Cloning into 'gh-pages'...
cp: cannot stat 'user_guide_src/_build/html/*': No such file or directory
##[error]Process completed with exit code 1.

@paulbalandan could you re-check ?

[paulbalandan]

That's strange. I'll dive into this later this evening. Thanks for the tip.