Bump xunit from 2.5.3 to 2.6.6

[dependabot[bot]]

Bumps xunit from 2.5.3 to 2.6.6.

Commits

• f03fe09 v2.6.6
• 280a0cb Update build to use .NET SDK 8 and C# 12 (#2863)
• fdf75ab #2334: Add assembly-level support for BeforeAfterTestAttribute (v2)
• ba06476 Add targetFramework for xunit.assert.nuspec
• 9db7d30 Test out additional target framework dependencies in .nuspec files
• 27e91e3 Bump up to 2.6.6-pre
• 7f82765 v2.6.5
• 98f19dd Updated tests (for analyzer exclusions)
• 298b1b1 #2854: Add constructors and AddRange for TheoryData<T>
• 36fe729 Bump up to v2.6.5-pre
• Additional commits viewable in compare view

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