Update AngleSharp to 1.7.3

[andregoepel]

Summary

• update the test-only AngleSharp dependency from 1.7.2 to 1.7.3
• regenerate locked restore files

Validation

• dotnet build
• dotnet test (42 passed)
• dotnet list package --vulnerable --include-transitive
• dotnet csharpier format .
• dotnet list package --outdated --format json

Closes #19