Update conditional install step typo in README.md

[alexaor]

Description

The example step for conditional workflow steps was incorrect

Motivation and Context

My pipeline kept installing dependencies on cache-hits when following the README.

How Has This Been Tested?

This change fixed my pipeline

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)
• [x] Documentation (add or update README or docs)

Checklist:

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