Keychron K8 ISO: Fix backlights lighting up rows on keypress

[warhuhn]

Description

Fixes issue #348.

I basically only added #define MATRIX_UNSELECT_DRIVE_HIGH to the config.h of the ISO version of the Keychron K8 config.

I only added this to the ISO version since i don't have a ANSI model to test and i don't know if the ANSI models even have this problem.

Types of Changes

• [ ] Core
• [x] Bugfix
• [ ] New feature
• [ ] Enhancement/optimization
• [x] Keyboard (addition or update)
• [ ] Keymap/layout/userspace (addition or update)
• [ ] Documentation

Issues Fixed or Closed by This PR

• 348

Checklist

• [x] My code follows the code style of this project: C, Python
• [x] I have read the PR Checklist document and have made the appropriate changes.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] I have tested the changes and verified that they work and don't break anything (as well as I can manage).