Fix test report by downgrading 'upload-artifact'

[FantasyTeddy]

This fixes the issue introduced with #28.
(It seems to be a known issue: dorny/test-reporter#343)

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 not work as expected).
• Performance improvement
• Refactoring (so no functional change)
• Other (docs, build config, etc)

Checklist:

• I've added tests for my code. (most of the time mandatory)
• I have added an entry to the changelog. (mandatory)
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[gasparnagy]

Thx. @FantasyTeddy I added you as collaborator, so you can make changes easier.

[FantasyTeddy]

Thank you, I'm looking forward to helping out wherever I can.