docs: use TS consistently in vitest instructions

[s-h-a-d-o-w]

What:

Since you're currently mentioning "./vitest.setup.ts", I figured that you're fine with using TS and this change does so consistently. (And once that is done, it's no longer necessary to add the setup file to the includes.)

Why:

Instructions are currently inconsistent.

Checklist:

• [x] Documentation
• [x] Tests N/A
• [x] Updated Type Definitions N/A
• [x] Ready to be merged