Avoid LD_LIBRARY_PATH in pynn-brainscales&hxtorch

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!243

We encountered build fails on some HPC sites due to openssl mismatches
between bare-metal tools and spack — especially curl and similar tools
for fetching.
Our build tool, waf, needs to find spack-provided libraries, e.g.
libclang.so, at runtime… so we will only set the environment variable
for this.

Add NEST 3.4_rc1

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!234

Add Neo v0.11.1 and fix missing dependency

Closes #26

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!217

add missing dependency for nixio

Closes #25

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!218

This reverts merge request !212

Re-try installing sda

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!212

minor fix (arbor version number)

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!210

bump LFPy-2.2.6 -> 2.3

Closes #22

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!209

Add Arbor v0.8.1

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!208

Script fixes

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!203

pin arbor to latest version

See merge request technical-coordination/project-internal/devops/platform/ebrains-spack-builds!204