Fixed CXX_API documentation error

[quazirafi]

PR Type

• [ ] Breaking change
• [ ] Feature
• [x] Patch

Brief Description

Fixes the issue: https://github.com/orgs/NWChemEx-Project/projects/16?pane=issue&itemId=18793368

Not In Scope

Anything not related to the above issue.

PR Checklist

• [x] Documentation (comments, API, user, design, and developer as applicable)
  • API
  • User
  • Design
  • Developer
• [x] Testing (unit, integration, performance, as applicable)
  • Unit
  • Integration
  • Performance
• [x] Code adheres to organization standards
  • C++
  • Python
  • Doxygen Conventions
  • reST Conventions

TODOs

Nothing.