Broke pin because of missing branch in atomic repo

[Fabien Chouteau]

Hi @JeremyGrosser,

I merged and removed the critical_sections branch of the atomic repo, so the the pin in alire.toml is broken:

rp2040_hal/alire.toml

Line 21 in 017bd3f

 atomic = { url='https://github.com/Fabien-Chouteau/atomic#critical_sections' }