Add tests for ThenInclude with TPH inheritance strategy.

[fiseni]

#463

[Copilot]

Pull Request Overview

This PR adds tests to verify that the Entity Framework Core query translation works correctly with TPH inheritance and ThenInclude. The key changes are:

• Introducing a new DbSet and configuration for the Bar entity and its derived types.
• Adding a TPH mapping in the DbContext for BarDerived.
• Implementing new tests in IncludeEvaluatorTests to compare query strings generated using inheritance-based navigation.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tests/Ardalis.Specification.EntityFrameworkCore.Tests/Fixture/TestDbContext.cs	Added DbSet for Bar and TPH mapping configuration for BarDerived.
tests/Ardalis.Specification.EntityFrameworkCore.Tests/Fixture/Data/Bar.cs	Added new classes (Bar, BarChild, BarDerived, BarDerivedInfo) for testing TPH inheritance.
tests/Ardalis.Specification.EntityFrameworkCore.Tests/Evaluators/IncludeEvaluatorTests.cs	Added tests checking the query translation for ThenInclude with TPH inheritance.

Comments suppressed due to low confidence (1)

tests/Ardalis.Specification.EntityFrameworkCore.Tests/Fixture/Data/Bar.cs:8

• Ensure that the project is targeting a C# version (such as C# 12) that supports collection expressions for List initializations to avoid potential compilation issues.

private readonly List<BarChild> _barChildren = [];