DM-41078: Add pytest configuration

[timj]

This prevents pytest from looking in parent directories.

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (9131c3c) 94.66% compared to head (f1b8f93) 94.84%.
Report is 23 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #3      +/-   ##
==========================================
+ Coverage   94.66%   94.84%   +0.17%     
==========================================
  Files          36       38       +2     
  Lines        4461     4730     +269     
==========================================
+ Hits         4223     4486     +263     
- Misses        238      244       +6     

Files	Coverage Δ
python/lsst/scarlet/lite/__init__.py	87.50% <100.00%> (+0.83%)	⬆️
python/lsst/scarlet/lite/component.py	96.89% <100.00%> (ø)
python/lsst/scarlet/lite/detect.py	100.00% <100.00%> (ø)
python/lsst/scarlet/lite/fft.py	94.70% <100.00%> (+0.03%)	⬆️
python/lsst/scarlet/lite/initialization.py	95.87% <100.00%> (+0.20%)	⬆️
python/lsst/scarlet/lite/models/free_form.py	94.73% <ø> (ø)
python/lsst/scarlet/lite/models/parametric.py	100.00% <100.00%> (ø)
python/lsst/scarlet/lite/source.py	98.24% <100.00%> (ø)
python/lsst/scarlet/lite/wavelet.py	95.65% <100.00%> (ø)
tests/test_blend.py	97.60% <100.00%> (+0.01%)	⬆️
... and 13 more

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[fred3m]

LGTM