Fix disable_highlight option

[cberner]

Fix the disable_highlight option, as it currently doesn't work

Description

Correctly check .Site params

Motivation and Context

It fixes the option, as it currently doesn't work

How Has This Been Tested?

I set disable_highlight = true, and checked that the Javascript is no longer included

Hugo Version:

Browser(s):

Screenshots (if appropriate):

Types of changes

• [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] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation, including theme.toml, accordingly.
• [x] I have read the Contributing Document.