Add note about IncludeTestAssembly default in MTP Code Coverage (#45521)

* Add note about IncludeTestAssembly default in MTP Code Coverage

* Update docs/core/testing/microsoft-testing-platform-extensions-code-coverage.md

Author: Youssef1313

docs/core/testing/microsoft-testing-platform-extensions-code-coverage.md

@@ -36,6 +36,9 @@ Microsoft Code Coverage provides the following options:
 
 For more information about the available options, see [settings](../additional-tools/dotnet-coverage.md#settings) and [samples](https://github.com/microsoft/codecoverage/tree/main/samples/Algorithms).
 
+> [!NOTE]
+> The default value of `IncludeTestAssembly` in Microsoft.Testing.Extensions.CodeCoverage is `true`, while it used to be `false` in VSTest. This means that test projects are excluded by default. For more information, see [Code Coverage configuration](https://github.com/microsoft/codecoverage/blob/main/docs/configuration.md).
+
 ## Coverlet
 
 > [!IMPORTANT]