Resolve bug in plugin-provided library sources requiring a `src` directory.

[steven-terrana]

PR Details

fixes #268

all credit goes to @connorh23 for finding the fix!

Description

The PluginLibraryProvider was mistaking checking if a library didn't have a src directory or a steps directory instead of checking that both don't exist.

How Has This Been Tested

error reproduced and fix validated manually.

Types of Changes

• [ ] Added Unit Testing
• [ ] Docs change / refactoring / dependency upgrade
• [x] 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)

Checklist

• [x] I have added the appropriate label for this PR
• [x] If necessary, I have updated the documentation accordingly.
• [x] All new and existing tests passed.