fix(run): add explicit nx dependency

[fahslaj]

Description

Adds an explicit dependency on Nx to @lerna/run.

Motivation and Context

#3481

How Has This Been Tested?

This has been tested manually against the repo from issue #3481 as well as a barebones reproduction workspace.

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 change)
• Chore (change that has absolutely no effect on users)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.