Fix consumption tax revenue calculation

[jdebacker]

This PR fixes the consumption tax revenue under differentiated goods specifications by passing the c_i object rather than the c_mat object in SS and TPI calculations.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.43%. Comparing base (b5a3ebd) to head (de7ede3).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
ogcore/TPI.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1074      +/-   ##
==========================================
- Coverage   72.44%   72.43%   -0.01%     
==========================================
  Files          21       21              
  Lines        5098     5100       +2     
==========================================
+ Hits         3693     3694       +1     
- Misses       1405     1406       +1     

Flag	Coverage Δ
unittests	72.43% <60.00%> (-0.01%)	⬇️

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

Files with missing lines	Coverage Δ
ogcore/SS.py	71.52% <100.00%> (+0.06%)	⬆️
ogcore/__init__.py	100.00% <100.00%> (ø)
ogcore/TPI.py	35.57% <0.00%> (-0.09%)	⬇️

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[jdebacker]

Local tests got cut off, but all tests for the affected files (SS.py and TPI.py) did pass:

tests/test_SS.py ...................................                       [  5%]
tests/test_TPI.py ...........................                              [ 10%]
tests/test_aggregates.py .........................................         [ 17%]
tests/test_basic.py ....                                                   [ 17%]