Fix education tax credit phase-out parameters

[martinholmer]

This pull request fixes two errors made in PR #2633:

• the 2022 value of ETC_pe_Single was incorrect (being set to $80K instead of $90K), and
• the value of the indexed attribute was not changed to false for the two ETC_pe_* parameters.

For details, see this section of the Internal Revenue Code and the fact that the values of the ETC_pe_* parameters are not mentioned in the IRS Rev. Proc. 2022-38 document containing 2023 values of inflation-indexed parameters.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.42%. Comparing base (728d81a) to head (923b4f2).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2790   +/-   ##
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  Coverage   99.42%   99.42%           
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  Files          13       13           
  Lines        2613     2613           
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  Hits         2598     2598           
  Misses         15       15           

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

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