fix: [#6825] Update xunit and fix compatibility issues in unit tests

[JhontSouth]

Addresses #6825

minor

Description

This PR updates xunit package version from 2.4.1 to 2.9.0 and applies the respective changes to meet the new version requirements.

Specific Changes

• Changed async void methods to async Task.
• Swapped assert equal parameters to leave the expected value in the correct argument position.
• Changed assert equal comparison of size collection 0 and 1 to Empty and Single methods.
• Added async operators instead of the use of Wait, GetAwaiter, and Result methods.

Testing

The following image shows the unit tests working in Net 6.0 and 8.0.

[tracyboehrer]

@JhontSouth Conflicts

[BruceHaley]

:heavy_check_mark: No Binary Compatibility issues for Microsoft.Bot.Builder.TemplateManager.dll :heavy_check_mark: No Binary Compatibility issues for Microsoft.Bot.Builder.Testing.dll :heavy_check_mark: No Binary Compatibility issues for Microsoft.Bot.Streaming.dll