Fix typo

What does this MR do?

This MR introduces a typo fix found on https://gitlab.com/gitlab-org/gitlab-runner/-/blob/main/docs/grit/_index.md?ref_type=heads&plain=0#delete-a-runner

The typo has been identified while reviewing the JA translated file in this Translation MR.

The localized file already had that typo fixed.

Why was this MR needed?

What's the best way to test this MR?

What are the relevant issue numbers?