Ignore pyproj to_proj4 warning when converting an AreaDefinition to a string

[djhoese]

This should resolve a majority of the warnings generated during pyresample and satpy tests. There are still many cases of tests using area_def.proj_str == other_area.proj_str, but we'll get to those later.

• [ ] Closes #xxxx
• [ ] Tests added
• [ ] Tests passed
• [ ] Passes git diff origin/main **/*py | flake8 --diff
• [ ] Fully documented

[codecov[bot]]

Codecov Report

Merging #512 (b2eab5e) into main (1357e3a) will decrease coverage by 0.01%. The diff coverage is 97.46%.

@@            Coverage Diff             @@
##             main     #512      +/-   ##
==========================================
- Coverage   94.32%   94.31%   -0.01%     
==========================================
  Files          79       79              
  Lines       12905    12936      +31     
==========================================
+ Hits        12172    12201      +29     
- Misses        733      735       +2     

Flag	Coverage Δ
unittests	94.31% <97.46%> (-0.01%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pyresample/future/geometry/area.py	100.00% <ø> (ø)
pyresample/utils/cf.py	90.17% <ø> (ø)
pyresample/gradient/__init__.py	95.16% <83.33%> (+0.01%)	:arrow_up:
pyresample/geometry.py	87.50% <95.65%> (-0.06%)	:arrow_down:
pyresample/area_config.py	90.44% <100.00%> (ø)
pyresample/geo_filter.py	100.00% <100.00%> (ø)
pyresample/test/test_geometry/test_area.py	99.19% <100.00%> (+0.01%)	:arrow_up:
pyresample/test/test_gradient.py	98.98% <100.00%> (ø)
pyresample/test/test_resample_blocks.py	98.62% <100.00%> (ø)
...le/test/test_resamplers/test_resampler_registry.py	96.55% <100.00%> (+0.63%)	:arrow_up:

[coveralls]

Coverage: 93.843% (-0.0007%) from 93.843% when pulling b2eab5e55664c7cde6f59fdfba22d728a8f8776e on djhoese:bugfix-ignore-proj-warn-areastr into 1357e3a8a362348190cd0f9df17ce28786368a27 on pytroll:main.