Enhance instructions for checking out pull requests locally

[maxhild]

Clarify instructions for fetching a pull request reference and creating a local branch.

Why:

Clarifying direction of merging and creation of new branches. I found it very hard to understand when first learning git and here it was unclear to me.

Closes:
#44014

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

I just added a small section. Thanks for providing open source code!

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.

[github-actions]

How to review these changes 👓

Thank you for your contribution. To review these changes, choose one of the following options:

• Spin up a codespace
• Set up a local development environment

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Table of review links

Note: Please update the URL for your staging server or codespace.

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
pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally.md	fpt ghec ghes@ 3.20 3.19 3.18 3.17 3.16 3.15 3.14	fpt ghec ghes@ 3.20 3.19 3.18 3.17 3.16 3.15 3.14

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

🤖 This comment is automatically generated.

[Sharra-writes]

@maxhild I'm relieved, because this is a much more narrowly scoped change than your issue suggested. When we say "section," we mean at least a paragraph with an H2 or H3 title above it, which would have been way too much. That said, while I think the sentence is fine to underscore the branch creation, I do think the example is excessive. If you take that out, I'll be happy to approve the clarification.