docs: update Twitter references to X (formerly Twitter)

[shivamk-29]

Why:

Closes: N/A

Twitter has rebranded to X. Updating these references to "X (formerly Twitter)" ensures that the user-facing documentation remains current, accurate, and easy to understand for global users.

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

Updated 4 documentation markdown files to replace outdated text references of "Twitter" with "X (formerly Twitter)". Additionally, updated a legacy example profile URL from https://twitter.com/github to https://x.com/github in the profile personalization guide to prevent documentation link rot.

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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🌱 First-Time Contributor Note:

I wanted to share that I actually noticed this outdated reference while going through the process of changing my own GitHub username! The documentation advised updating other social profiles like LinkedIn and Twitter, which made me realize the text was out of date. Since this is my very first open-source commit, I utilized AI to help me safely navigate the Git workflow, filter out underlying system/API files, and ensure I was only touching documentation prose. Excited to submit my first contribution here!

[github-actions]

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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
account-and-profile/concepts/username-changes.md	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17
account-and-profile/tutorials/personalize-your-profile.md	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17
organizations/managing-organization-settings/renaming-an-organization.md	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17	fpt ghec ghes@ 3.21 3.20 3.19 3.18 3.17
site-policy/privacy-policies/github-general-privacy-statement.md	fpt	fpt

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

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