Use git@version syntax for spack pipelines and buildcache

[cameronrutherford]

spack/spack#43859

spack/spack#38484 (comment)

Previously the git version feature of spack was a little buggy, and so this feature wasn't possible. Now that spack is able to handle this, we should attempt to properly version our packages in the GHCR based on the git branch.

This can also be extended to ReSolve and HiOp..