chore: Removes unneeded forwardRef from stsn test helper

[pan-kot]

Addressing this finding: 15f08d8#r167576586

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[codecov]

Codecov Report

❌ Patch coverage is 95.45455% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 98.78%. Comparing base (6efdfb4) to head (676cf7c).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...rc/internal/single-tab-stop/test-helpers/index.tsx	95.45%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #167   +/-   ##
=======================================
  Coverage   98.78%   98.78%           
=======================================
  Files          36       36           
  Lines         904      904           
  Branches      256      243   -13     
=======================================
  Hits          893      893           
- Misses         10       11    +1     
+ Partials        1        0    -1     

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