Closes #4563: Upgrade Drupal core to 10.6.x. (2.x only)

[joeparsons]

Description

Drupal 10.6.x release notes:

• https://www.drupal.org/project/drupal/releases/10.6.0
• https://www.drupal.org/project/drupal/releases/10.6.1
• https://www.drupal.org/project/drupal/releases/10.6.2

NOTE: We don't actually want to include this change in a Quickstart 2 release until we have a Quickstart 3 release with Drupal 11.3 available since sites running Drupal 10.6.x can only upgrade to Drupal 11.3.0+.
(i.e. this PR is blocked by #5043)

Release notes

Quickstart 2 has been upgraded to Drupal 10.6.x. Security support for Quickstart 2 and Drupal 10 will end after December 2026. Owners of Quickstart 2 sites that have not begun preparing for the upgrade to Quickstart 3 and Drupal 11+, should start making preparations as soon as possible.

Related issues

Closes #4563

How to test

General / smoke testing.

Types of changes

Arizona Quickstart (install profile, custom modules, custom theme)

• Patch release changes
  • Bug fix
  • Accessibility, performance, or security improvement
  • Critical institutional link or brand change
  • Adding experimental module
  • Update experimental module
• Minor release changes
  • New feature
  • Breaking or visual change to existing behavior
  • Upgrade experimental module to stable
  • Enable existing module by default or database update
  • Non-critical brand change
  • New internal API or API improvement with backwards compatibility
  • Risky or disruptive cleanup to comply with coding standards
  • High-risk or disruptive change (requires upgrade path, risks regression, etc.)
• Other or unknown
  • Other or unknown

Drupal core

• Patch release changes
  • Security update
  • Patch level release (non-security bug-fix release)
  • Patch removal that's no longer necessary
• Minor release changes
  • Major or minor level update
• Other or unknown
  • Other or unknown

Drupal contrib projects

• Patch release changes
  • Security update
  • Patch or minor level update
  • Add new module
  • Patch removal that's no longer necessary
• Minor release changes
  • Major level update
• Other or unknown
  • Other or unknown

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My change requires release notes.