Fix probable typo in JSON example

[yaakov-h]

Why:

this is lowercase in RFC 8693

Closes: #38623

What's being changed (if available, include any code snippets, screenshots, or gifs):

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• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

[Copilot]

Pull Request Overview

This PR corrects the casing of a JSON property in the OIDC example to align with RFC 8693.

• Lowercases the Issued_token_type key to issued_token_type in the JSON snippet.

[github-actions]

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Source	Review	Production	What Changed
copilot/building-copilot-extensions/using-oidc-with-github-copilot-extensions.md	fpt ghec	fpt ghec

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🤖 This comment is automatically generated.

[Sharra-writes]

Thanks for opening a PR! Let me check on this since these things are case sensitive.

[Sharra-writes]

Okay, confirmed that it should be lower case. I'll get this merged once checks are passing!

[github-actions]

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