Mentions are not rewritten by GitHub Enterprise Importer (#59122)

Co-authored-by: Felix Guntrip <guntrip@github.com>
Co-authored-by: Dean Tambling <tambling@github.com>
Co-authored-by: mc <42146119+mchammer01@users.noreply.github.com>

Author: 4 people

data/reusables/enterprise-migration-tool/data-not-migrated.md

@@ -11,6 +11,7 @@
 * GitHub Apps and GitHub App installations
 * {% data variables.large_files.product_name_short %} objects and large binaries (repositories using {% data variables.large_files.product_name_short %} are still supported, see [Limitations of {% data variables.product.prodname_importer_proper_name %}](#limitations-of-github-enterprise-importer))
 * Links from commits to pull requests that were rebase merged
+* Mentions of users, teams, and organizations in pull request, issue, release, and comment bodies (the username originally mentioned is retained)
 * Packages in {% data variables.product.prodname_registry %}{% ifversion projects-v1 %}
 * Projects (classic) at the organization level{% endif %}
 * {% data variables.product.prodname_projects_v2 %} (the new projects experience)