[steps] Composite functions: skip the outputs step when the call never ran

[sswrk]

Why

In this comment #4062 (comment) it was brought up that when no steps of a composite function run (because an earlier step has failed) and the caller sets if: ${{ always() }}, the synthetic "outputs" step runs anyway.

The expected behavior is that the synthetic "outputs" step is skipped too.

How

In CompositeBuildStep, shouldExecuteStep is overridden so the outputs step runs if runByDefault is true or any authored child has run.

Test Plan

Added unit tests.

[linear-code]

ENG-25537

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.53%. Comparing base (a9d693d) to head (a85cf6e).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4207      +/-   ##
==========================================
+ Coverage   63.52%   63.53%   +0.02%     
==========================================
  Files        1028     1028              
  Lines       46918    46938      +20     
  Branches     9847     9852       +5     
==========================================
+ Hits        29801    29819      +18     
- Misses      17015    17017       +2     
  Partials      102      102              

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[github-actions]

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