[release] v7.6.0

[toxa81]

TODO:

• check that spack recipe is up-to-date; as soon as we tag a new version, it should be added to spack recipe and pushed to the main spack repo @simonpintarelli @RMeli
• merge pending PRs ([fix] need to call init_atoms_to_grid_idx() only in magnetic case #1011)
• and this PR ([fix] sirius_add_hubbard_atom_pair API function #1015)
• check that cp2k works and also UPF-v2 files can be used in cp2k input @mtaillefumier
• any other small changes that can be incorporated?

[mtaillefumier]

cp2k is ready for the new release. the toolchain is updated as well. Just need to update the spack recipe

[abussy]

It would be nice if we squeeze PR #1016 in this release. We are getting close to a first integration of SIRIUS in DFTK, and the changes to the API will need to be officially released in order to create a SIRIUS.jl package.

[mtaillefumier]

I am good with it as soon as this PR is ready for merging. I will update cp2k build system after the tag is created.

[RMeli]

Happy to help with the Spack package(s) once the release is done.

[simonpintarelli]

I've added an update related to spla (copied from spack upstream). The rest looks good to me.