Yu Watanabe e7485799a4 semaphore: use Ubuntu 24.04 ...

Semaphore CI/CD now emits the following error.
```
OS image 'ubuntu2004' for machine type 'e1-standard-2' is currently in a brownout phase.
Please use another OS image.
```
Let's use newer image.

2026-03-10 00:47:53 +00:00

..

semaphore-runner.sh

semaphore: switch to debian stable

2026-02-25 23:31:54 +00:00

semaphore.yml

semaphore: use Ubuntu 24.04

2026-03-10 00:47:53 +00:00