fix(apple): Fix undefined variable in config block

[rromanchuk]

DESCRIBE YOUR PR

Example does not compile. Align yielded block variable name in scope and match objective-c name

IS YOUR CHANGE URGENT?

None: Not urgent, can wait up to 1 week+

SLA

• Teamwork makes the dream work, so please add a reviewer to your PRs.
• Please give the docs team up to 1 week to review your PR unless you've added an urgent due date to it.
  Thanks in advance for your help!

PRE-MERGE CHECKLIST

Make sure you've checked the following before merging your changes:

• Checked Vercel preview for correctness, including links
• PR was reviewed and approved by any necessary SMEs (subject matter experts)
• PR was reviewed and approved by a member of the Sentry docs team

LEGAL BOILERPLATE

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[vercel]

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