docs: Update macos.md visual tests initial setup --bin path (#46428)

Iago Bermúdez created 

Two days ago, `macos.md` was updated, changing the --bin name from
visual_test_runner to zed_visual_test_runner. This was updated for the
**Updating baselines** section, but not for **Initial setup** I just
updated it.

Release Notes:
- N/A

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