ENH: Output anatomical coregistration transforms, if generated

[mgxd]

This re-enables saving the T1-T2 coregistration, if both are present.

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 56.45%. Comparing base (ffc69a8) to head (1edb875).
Report is 28 commits behind head on master.

Files with missing lines	Patch %	Lines
nibabies/workflows/anatomical/fit.py	40.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #437      +/-   ##
==========================================
+ Coverage   55.89%   56.45%   +0.55%     
==========================================
  Files          69       70       +1     
  Lines        6689     6719      +30     
  Branches      832      828       -4     
==========================================
+ Hits         3739     3793      +54     
+ Misses       2745     2717      -28     
- Partials      205      209       +4     

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