Update branch protection rule instructions

[ashis-baral]

Why:

Closes: #45675

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

Updated the branch protection rule instructions to match the current GitHub UI.

Changed the step from:

Next to "Branch protection rules", click Add rule.

to:

Under "Branch protection rules", click Add classic branch protection rule.

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]

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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
repositories/configuring-branches-and-merges-in-your-repository/managing-protected-branches/managing-a-branch-protection-rule.md	fpt ghec ghes@ 3.22 3.21 3.20 3.19 3.18 3.17	fpt ghec ghes@ 3.22 3.21 3.20 3.19 3.18 3.17	from reusable

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

🤖 This comment is automatically generated.

[SunShineHead]

Na

[subatoi]

Thanks again, @ashis-baral—this also looks good so I'll get this merged now 🙇

[github-actions]

Thanks very much for contributing! Your pull request has been merged 🎉 You should see your changes appear on the site in approximately 24 hours. If you're looking for your next contribution, check out our help wanted issues ⚡

[ashis-baral]

@subatoi Thank you so much for the review and for getting this merged.😊