docs(migrations): update ado2gh PAT scopes for mannequin retrieval

[Srujanreddy1234]

Why:

Closes #45071

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

Updated the required Personal Access Token (PAT) scopes for the ado2gh CLI tool when retrieving or reclaiming mannequins. Relying strictly on admin:org triggers a FORBIDDEN permission error. The documentation has been updated to explicitly specify that repo, admin:org, and workflow scopes are required for this action to succeed.

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

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
migrations/ado/manage-access.md	fpt ghec	fpt ghec	from reusable
migrations/using-github-enterprise-importer/migrating-from-bitbucket-server-to-github-enterprise-cloud/managing-access-for-a-migration-from-bitbucket-server.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	from reusable

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

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[Sharra-writes]

@Srujanreddy1234 There's already a PR open for this, and it's not even certain we want to change it yet. Please wait until issues have a help wanted tag to open PRs for them.