fix: add taproot key only

[theacdutra]

Description

Add taproot key in derive method.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 1.6%. Comparing base (5a05fcc) to head (9648aa2).
Report is 11 commits behind head on v0.12.

Files with missing lines	Patch %	Lines
src/descriptor.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##           v0.12   #281     +/-   ##
======================================
- Coverage    1.7%   1.6%   -0.1%     
======================================
  Files          8      8             
  Lines        638    677     +39     
======================================
  Hits          11     11             
- Misses       627    666     +39     

Flag	Coverage Δ
rust	1.6% <0.0%> (-0.1%)	⬇️

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[dr-orlovsky]

ACK 9648aa2