Fix Gitaly max_queue_wait TOML config

What does this MR do?

This fixes an invalid TOML config introduced in !5892 (merged).

Related issues

gitlab#353875 (closed)

Checklist

See Definition of done.

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Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
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