[python] Normalize unit-test exception coverage

[johnkerl]

As we run our unit tests on more and more environments, including on-image from docker run, we more often run into an old unit-test error. Namely, apis/python/tests/test_dataframe_index_columns.py::test_types_read_errors may either throw RuntimeError or tiledb.cc.TileDBError. Yet we only catch the former. This means, for example, when running unit tests from docker run we need to mentally 'subtract out' these spurious fails. (This has already bitten developers, who have become used to it.) What we should be doing is catching both. (Also note: grepping for RuntimeError in apis/python/tests show we already do this in other unit-test files -- we need to do it in one more.)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (af10674) 62.75% compared to head (fdc05ed) 89.61%.

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Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1909       +/-   ##
===========================================
+ Coverage   62.75%   89.61%   +26.86%     
===========================================
  Files         106       34       -72     
  Lines       10014     3592     -6422     
===========================================
- Hits         6284     3219     -3065     
+ Misses       3730      373     -3357     

Flag	Coverage Δ
python	89.61% <ø> (+0.68%)	⬆️
r	?

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[nguyenv]

Potentially corrected here and here in #1793 where we translate RuntimeError to SOMAError. Approving this PR in the interim before #1793 gets merged.