handlebars_admin_menu cannot be installed on Drupal 12 until its dependencies release

Title: handlebars_admin_menu cannot be installed on Drupal 12
until its dependencies release

Problem/Motivation

>#3610218 >
takes Handlebars to Drupal 12. The main module and the
handlebars_commerce example install and work there, but
handlebars_admin_menu does not, because neither of its
dependencies has a Drupal 12 release yet:

• restui — latest is
  8.x-1.22, ^9.5 || ^10 || ^11
• rest_menu_items
  — latest is 3.0.7, ^10 || ^11

The example module declares ^10.3 || ^11 || ^12 along with the
rest of the project, so it is not marked incompatible forever, but Drupal will
refuse to enable it on 12 until the dependencies are satisfiable. That is the
correct behaviour and there is nothing to fix here — this issue exists so the
blocker is visible rather than being rediscovered later.

Proposed resolution

Wait for both to release for Drupal 12. Both already have automated
compatibility issues open, and both are close:

• >restui #3602536 >
  — Needs review. The merge request is five files and the bot did update the
  info.yml, so Upgrade Status considers it compatible.
• >rest_menu_items #3602521 >
  — Needs review. The merge request is two lines, both info.yml version bumps.

Neither needs code written. What they need is somebody to test them and say so
in the issue, so a maintainer can merge and cut a release. Worth doing that
rather than only waiting.

Remaining tasks

• Test both merge requests on Drupal 12 and report the results upstream.
• Once both have a Drupal 12 release, install
  handlebars_admin_menu on 12 and confirm the decoupled admin
  menu example still renders.
• Close this issue when that is done.

Not a blocker for the main module.
>#3610218 >
can go ahead without this.