Resolve IL2091 warnings

[martincostello]

Resolve two AoT warnings on OutcomePipelineBuilderExtensions found by following the instructions in #1737 (comment).

Relates to #1732.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (95b217b) 84.56% compared to head (c297f31) 84.56%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1744   +/-   ##
=======================================
  Coverage   84.56%   84.56%           
=======================================
  Files         307      307           
  Lines        6790     6790           
  Branches     1043     1043           
=======================================
  Hits         5742     5742           
  Misses        839      839           
  Partials      209      209           

Flag	Coverage Δ
linux	84.56% <ø> (ø)
macos	84.56% <ø> (ø)
windows	84.56% <ø> (ø)

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Files	Coverage Δ
...Simmy/Outcomes/OutcomePipelineBuilderExtensions.cs	100.00% <ø> (ø)

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