Raise warnings as errors in the test suite

[vyasr]

Description

This PR fixes a final few warnings introduced in PRs merged after #12406 or with changes that weren't merged into #12406. More importantly, this PR updates the testing suite to always raise uncaught warnings as errors. This is a substantial change to the testing suite that will allow us to proactively react to deprecations in our dependencies, identify areas where pandas/pyarrow/some other dependency handles input data in different ways than us, etc. I've opted for the strictest possible setting, but am open to reviewer requests to be a little more lax with certain classes of warnings.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[codecov]

Codecov Report

Base: 86.58% // Head: 85.69% // Decreases project coverage by -0.88% ⚠️

Coverage data is based on head (a3e825a) compared to base (b6dccb3).
Patch has no changes to coverable lines.

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-23.02   #12468      +/-   ##
================================================
- Coverage         86.58%   85.69%   -0.89%     
================================================
  Files               155      155              
  Lines             24368    24798     +430     
================================================
+ Hits              21098    21250     +152     
- Misses             3270     3548     +278     

Impacted Files	Coverage Δ
python/cudf/cudf/_version.py	1.41% <0.00%> (-98.59%)	⬇️
python/cudf/cudf/core/buffer/spill_manager.py	72.50% <0.00%> (-7.50%)	⬇️
python/cudf/cudf/core/buffer/spillable_buffer.py	90.04% <0.00%> (-2.81%)	⬇️
python/cudf/cudf/utils/dtypes.py	77.77% <0.00%> (-1.69%)	⬇️
python/cudf/cudf/options.py	86.11% <0.00%> (-1.59%)	⬇️
python/cudf/cudf/core/single_column_frame.py	94.30% <0.00%> (-1.27%)	⬇️
...ython/custreamz/custreamz/tests/test_dataframes.py	98.38% <0.00%> (-1.01%)	⬇️
python/dask_cudf/dask_cudf/io/parquet.py	91.81% <0.00%> (-0.59%)	⬇️
python/cudf/cudf/core/multiindex.py	91.66% <0.00%> (-0.51%)	⬇️
python/cudf/cudf/core/algorithms.py	90.00% <0.00%> (-0.48%)	⬇️
... and 36 more

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[vyasr]

/merge