Clarify short title of "Using custom instructions to unlock the power of Copilot code review"

[divigrape9]

proposing a short title that better indicate the purpose of this section

Why:

Currently the short title of this tutorial is "Use custom instructions"; which doesn't indicate this tutorial is related to Code Review.

This is misleading when navigating through the tutorials from the side navigation:

Closes: #43752

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

I'm only proposing a change to the Short Title of this article.

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• 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.

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Table of review links

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The table shows the files in the content directory that were changed in this pull request. This helps you review your changes on a staging server. Changes to the data directory are not included in this table.

Source	Review	Production	What Changed
copilot/tutorials/use-custom-instructions.md	fpt ghec	fpt ghec

Key: fpt: Free, Pro, Team; ghec: GitHub Enterprise Cloud; ghes: GitHub Enterprise Server

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[Sharra-writes]

@divigrape9 The issue here is that the short title affects the URL, and it may also have a word limit that we can bypass but an open source contributor can't. I'll take your issue to the team and see what they want to do, if anything, but it will probably need to be fixed internally if we change it, since changing it will also affect redirects.

[Sharra-writes]

@divigrape9 We are going to update the short title, but it does need to be done internally. We have a PR open for it, so I'm going to close this one. Thanks for flagging it!