Publish Ubuntu 24.04 base, Hub, and Editor images

## Problem

GameCI's current Ubuntu image chain is based on Ubuntu 22.04 (`glibc` 2.35). Native Unity plugins built for Ubuntu 24.04 can therefore fail during asset import before project code or runtime fallbacks can run.

A concrete example is Rive Unity: its Linux `librive.so` requires `GLIBC_2.38`, while Rive officially documents Linux support as Vulkan on Ubuntu 24.04+:

- https://rive.app/docs/game-runtimes/unity
- https://github.com/rive-app/rive-unity/issues/156

The failure occurs while Unity's `ScriptedImporter` loads the native library, so changing the outer GitHub runner OS does not help; the compatibility boundary is the nested `unityci/editor` container.

## Request

Could GameCI publish an Ubuntu 24.04 image chain for:

- `unityci/base`
- `unityci/hub`
- `unityci/editor`

Ideally this would be introduced as a new image major version or parallel tag family so existing Ubuntu 22.04 consumers do not move implicitly.

## Validation considerations

The migration should cover at least:

- base Editor / test-runner use
- Android modules
- iOS modules
- Linux modules
- Unity activation and Hub installation
- Burst/IL2CPP and common render-pipeline projects

I am happy to contribute an initial PR and validate it against Unity 6000.5.7f1 with GameCI's builder and test-runner actions.

Start by examining the existing unityci/base, unityci/hub, and unityci/editor image chain and the GameCI builder and test-runner actions. Compare the Ubuntu 22.04 assumptions with the requested Ubuntu 24.04 chain, then validate Unity 6000.5.7f1 across Editor/test-runner, Android, iOS, Linux, activation, Hub, Burst/IL2CPP, and render-pipeline use cases without changing existing consumers implicitly.

Written by the indexing model from the issue text.