raise_warning -> new SchemaWarning not UserWarning

[nathanjmcdougall]

#1297

The new SchemaWarning is a subclass of UserWarning, so I think this means it shouldn't cause too many backward compatibility issues. I have added some tests that check the old behaviour still works.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (c1f9863) 93.82% compared to head (30716ab) 93.82%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1298   +/-   ##
=======================================
  Coverage   93.82%   93.82%           
=======================================
  Files          90       90           
  Lines        6704     6705    +1     
=======================================
+ Hits         6290     6291    +1     
  Misses        414      414           

Files Changed	Coverage Δ
pandera/api/checks.py	98.52% <ø> (ø)
pandera/api/hypotheses.py	100.00% <ø> (ø)
pandera/backends/pandas/builtin_checks.py	95.52% <ø> (ø)
pandera/backends/pandas/base.py	100.00% <100.00%> (ø)
pandera/backends/pyspark/base.py	100.00% <100.00%> (ø)
pandera/errors.py	100.00% <100.00%> (ø)

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[cosmicBboy]

thanks @nathanjmcdougall 🚀