[CI/CD] The pipelines currently are not working with PETSc 3.20

[sblauth]

Currently, cashocs workflows are not running correctly due to a recent update to PETSc 3.20 which is available on conda-forge. Most of the required patches have already been applied in the petsc320fix branch https://github.com/sblauth/cashocs/tree/petsc320fix

However, one issue remains, with the PETScDMCollection and its transfer matrix, see conda-forge/fenics-feedstock#192

For the moment, we leave this in the main development version, expecting a quick fix. If this cannot be done as fast as expected, we should, for the moment, pin PETSc to <=3.19

[sblauth]

We have pinned PETSc to version <= 3.19 in the conda-forge feedstock, see conda-forge/cashocs-feedstock#84.
Once the issues with PETSc 3.20 are fixed, the pin should be removed here as well as in the conda-forge feedstock.