tests: Miscellaneous fixes for the test suite

[JDBetteridge]

Encountered when running outside of CI

[codecov]

Codecov Report

❌ Patch coverage is 57.89474% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.53%. Comparing base (ce52ad1) to head (e041b0c).

Files with missing lines	Patch %	Lines
conftest.py	50.00%	2 Missing and 1 partial ⚠️
tests/test_mpi.py	25.00%	3 Missing ⚠️
devito/logger.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2929      +/-   ##
==========================================
- Coverage   83.55%   83.53%   -0.03%     
==========================================
  Files         257      257              
  Lines       53526    53536      +10     
  Branches     4583     4584       +1     
==========================================
- Hits        44726    44722       -4     
- Misses       8007     8019      +12     
- Partials      793      795       +2     

Flag	Coverage Δ
pytest-gpu-aomp-amdgpuX	68.37% <45.45%> (+<0.01%)	⬆️
pytest-gpu-gcc-	78.39% <52.63%> (-0.02%)	⬇️
pytest-gpu-icx-	78.33% <57.89%> (-0.03%)	⬇️
pytest-gpu-nvc-nvidiaX	69.03% <45.45%> (-0.01%)	⬇️

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[FabioLuporini]

I don't think this is needed, and in general, it seems off to have such an option in configuration

I'm not even sure I understand the comment above...

Why can we not use a combo of skipif and platform instead?

[JDBetteridge]

It was needed because it was taking out my local machine!
Relevant discussion: https://devitocodes.slack.com/archives/C7JMLMSG0/p1778763735024689