Add known values of 2024 policy parameters

[martinholmer]

Fixes #2814.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.42%. Comparing base (76ccd83) to head (ed04e7a).
Report is 6 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2816   +/-   ##
=======================================
  Coverage   99.42%   99.42%           
=======================================
  Files          13       13           
  Lines        2613     2613           
=======================================
  Hits         2598     2598           
  Misses         15       15           

Flag	Coverage Δ
unittests	99.42% <100.00%> (ø)

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Files with missing lines	Coverage Δ
taxcalc/__init__.py	100.00% <100.00%> (ø)
taxcalc/policy.py	100.00% <100.00%> (ø)