Fix spack test

[BenjaminRodenberg]

Currently the test for our spack build is broken: https://github.com/precice/python-bindings/blob/develop/.github/workflows/build-spack.yml

I think the test is generally useful, because we often had the situation that we just realized that the spack package is broken or outdated just after the actual release. This led to delays and stressful situations. Unfortunately maintaining the spack test is very tedious and requires quite some knowledge on spack. Since there is currently no possibility to maintain this test, we decided to ignore it and I will soon deactivate it to avoid the failure notification.