Migrate to xunit v3

[martincostello]

Migrate to xunit v3.

Copilot reviewed 5 out of 14 changed files in this pull request and generated no comments.

Files not reviewed (9)

• Directory.Build.props: Language not supported
• Directory.Packages.props: Language not supported
• samples/TodoApp.Tests/TodoApp.Tests.csproj: Language not supported
• tests/SqlLocalDb.Tests/MartinCostello.SqlLocalDb.Tests.csproj: Language not supported
• tests/SqlLocalDb.Tests/DelayedMessageBus.cs: Evaluated as low risk
• tests/SqlLocalDb.Tests/RetryFactDiscoverer.cs: Evaluated as low risk
• tests/SqlLocalDb.Tests/RetryTestCase.cs: Evaluated as low risk
• src/SqlLocalDb/SqlLocalDbErrors.cs: Evaluated as low risk
• samples/TodoApp.Tests/TodoRepositoryTests.cs: Evaluated as low risk

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.61%. Comparing base (a487408) to head (5eaa065).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1061      +/-   ##
==========================================
- Coverage   91.69%   91.61%   -0.09%     
==========================================
  Files          22       22              
  Lines        1204     1204              
  Branches      122      122              
==========================================
- Hits         1104     1103       -1     
  Misses         72       72              
- Partials       28       29       +1     

Flag	Coverage Δ
linux	57.14% <ø> (+0.66%)	⬆️
macos	56.81% <ø> (ø)
windows	90.86% <ø> (-0.17%)	⬇️

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