Bump xunit from 2.5.0 to 2.6.1

[dependabot[bot]]

Bumps xunit from 2.5.0 to 2.6.1.

Commits

• 9f1684f v2.6.1
• 5d9ef4b Remove unnecessary XUNIT_VALUETASK definition
• 0266bac Latest assertions
• fb3c3cf Remove all ValueTask support from assertions
• 801790c Reconcile AcceptanceTestAssembly and friends with v3
• f244cc8 More shared assertion tests that shouldn't return ValueTask
• 262dd72 Shared assertion tests cannot return ValueTask
• 36bbf77 Bump up to v2.6.1-pre
• 6a07b95 v2.6.0
• 5a7297e #2806: Performance improvements in Assert.Equal (v2)
• Additional commits viewable in compare view

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