Fix alert header

[akordowski]

Why:

Fix alert header to match the text.

Closes: #35519

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

The alert header has been changed from tip to warning to better match the text.

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 a 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.

[github-actions]

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The table contains an overview of files in the content directory that have been changed in this pull request. It's provided to make it easy to review your changes on the staging site. Please note that changes to the data directory will not show up in this table.

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Content directory changes

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Source	Preview	Production	What Changed
organizations/managing-oauth-access-to-your-organizations-data/about-oauth-app-access-restrictions.md	fpt ghec	fpt ghec

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

[nguyenalex836]

@akordowski Getting this merged! ✨

[github-actions]

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