Fix bug in extension anv-spintevolve-3d

[lang-m]

• Reported in https://github.com/oommf-extensions/anv-spintevolve-3d/issues/1
• failed also in https://github.com/ubermag/oommfc/actions/runs/9928523980/job/27755381956?pr=133 (oommfc with latest OOMMF from this repository, compiled as part of the CI)

The fixes are based on the changes 2.0b0 -> 2.1a0 in the (non-3d) anv_spintevolve extension coming with OOMMF.

@fangohr Could you please update (overwrite) the docker container for OOMMF 2.1a0 after merging this.

The fixes in this PR are required for https://github.com/ubermag/oommfc/pull/133

[lang-m]

@fangohr Please merge if approving.

[fangohr]

Docker images on DockerHub are updated.