[FIX] Constrain threading for intramodal template

[mattcieslak]

Intramodal template was using too many threads and making HPCs unhappy.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 28.13%. Comparing base (8802df4) to head (52a21ab).

Files with missing lines	Patch %	Lines
qsiprep/interfaces/ants.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #825      +/-   ##
==========================================
+ Coverage   28.12%   28.13%   +0.01%     
==========================================
  Files          69       69              
  Lines       10079    10082       +3     
  Branches     1302     1107     -195     
==========================================
+ Hits         2835     2837       +2     
- Misses       7146     7147       +1     
  Partials       98       98              

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