Enforce(meta-brainscales) pynn@0.9.4 or later

BrainScaleS' PyNN depends on PyNN.serialization… which is only available at 0.9.4 or later…

mentioned in commit f146a1a6

merged

Thanks for merging, but it looks weird…

==> Installing environment ebrains-spack-builds
==> All of the packages are already installed

and there's no py-pynn > 0.9.1 installed:

sh-4.2$ ls /srv/test-build/spack/opt/spack/linux-centos7-broadwell/gcc-10.3.0/py-pynn-* -lisad
9578908 4 drwxr-sr-x. 4 1000410000 65534 4096 Jul 20 16:39 /srv/test-build/spack/opt/spack/linux-centos7-broadwell/gcc-10.3.0/py-pynn-0.9.1-ibzafxztvmnkycibo6jwprhhojqj6ggt

I'll try to also pin the py-pynn in spack.yaml — maybe there is a problem with the early concretization.

mentioned in merge request !18 (merged)

In all probability spack found pynn already installed and did not do anything. Now, in the new MR probably the rebuild will be triggered