FIX: Issues with PETSc 3.20

[sblauth]

This PR fixes some issues when using PETSc >= 3.20 as linear algebra backend.

Most issues were coming from a suboptimal use of PETSc.Vec.aypx, replacing this with PETSc.Vec.axpby fixes these issues.
However, there is still an issue with the interpolator or fenics.PETScDMCollection, which has not yet been fixed. This issue is not yet fixed / adressed, see #320.
As soon as the issue is fixed (in FEniCS), we can remove the pin from the PETSc version.

[codecov]

Codecov Report

Merging #321 (a668410) into hotfix/2.0.12 (1c4b100) will increase coverage by 0.01%.
The diff coverage is 95.00%.

❗ Current head a668410 differs from pull request most recent head 77f5ccd. Consider uploading reports for the commit 77f5ccd to get more accurate results

@@                Coverage Diff                @@
##           hotfix/2.0.12     #321      +/-   ##
=================================================
+ Coverage          92.66%   92.66%   +0.01%     
=================================================
  Files                 83       83              
  Lines               6440     6445       +5     
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+ Hits                5967     5972       +5     
  Misses               473      473              

Files	Coverage Δ
...cs/_optimization/optimization_algorithms/l_bfgs.py	99.40% <100.00%> (+0.01%)	⬆️
.../shape_optimization/shape_variable_abstractions.py	91.89% <100.00%> (ø)
...gy_optimization/topology_optimization_algorithm.py	87.03% <100.00%> (+0.21%)	⬆️
cashocs/space_mapping/optimal_control.py	88.66% <100.00%> (ø)
cashocs/space_mapping/shape_optimization.py	85.71% <75.00%> (ø)

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