Updated Fusion-vnext test projects to use xUnit v3 instead of TUnit

[glen-84]

Summary of the changes (Less than 80 chars)

• Updated Fusion-vnext test projects to use xUnit v3 instead of TUnit.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.38%. Comparing base (91b8977) to head (170f69c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7847      +/-   ##
==========================================
- Coverage   74.38%   74.38%   -0.01%     
==========================================
  Files        2876     2876              
  Lines      150071   150071              
  Branches    17450    17450              
==========================================
- Hits       111631   111629       -2     
- Misses      32622    32627       +5     
+ Partials     5818     5815       -3     

Flag	Coverage Δ
unittests	74.38% <ø> (-0.01%)	⬇️

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