Fix outdated-release-phase-terminology warnings (#58306)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

data/variables/projects.yml

@@ -26,4 +26,4 @@ legacy_archived_item_limit: '10,000'
 issue_type_limit: '25'
 sub-issue_limit: '100'
 
-tasklists: 'tasklists (beta)'
+tasklists: 'tasklists ({% data variables.release-phases.public_preview %})'

data/variables/release-phases.yml

@@ -1,6 +1,8 @@
 # Contains variables to identify GitHub's release phases. These are aligned with Microsoft standards.
 # For reference: https://github.com/github/docs-team/issues/4302
 
+preview: 'preview'
+
 public_preview: >-
   {% ifversion ghes < 3.16 %}beta{% else %}public preview{% endif %}