fix: correct return tuple for Enzyme's reverse autodiff

[gdalle]

Fixes #1875

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.96%. Comparing base (b39a1fc) to head (5cb9400).
⚠️ Report is 190 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1888      +/-   ##
==========================================
+ Coverage   68.16%   69.96%   +1.79%     
==========================================
  Files         109      120      +11     
  Lines       11779    13044    +1265     
==========================================
+ Hits         8029     9126    +1097     
- Misses       3750     3918     +168     

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