[Bug]: GenerateAssertion extension not available when targeting concrete collection

[ascott18]

Description

The following generated assertion is not available because of a type mismatch between the generated extension ContainsMessage(this IAssertionSource<string[]> source, ...) and the actual return type of Assert.That(), which is CollectionAssertion<string>.

public class UnitTest1
{
    [Test]
    public async Task Test1()
    {
        string[] items = new[] { "food", "bard" };
        await Assert.That(items).ContainsMessage("foo", false);
    }
}

public static partial class Assertions
{
    [EditorBrowsable(EditorBrowsableState.Never)]
    [GenerateAssertion(ExpectationMessage = "to contain message '{needle}'")]
    public static bool ContainsMessage(this string[] strings, string needle, bool exact = true)
    {
        return strings.Any(x => exact ? x == needle : x.Contains(needle));
    }
}

Expected Behavior

Generated assertion is available when assertion target is a concrete collection.

Actual Behavior

Assertion not available.

Steps to Reproduce

See above code.

TUnit Version

1.15.0

.NET Version

.NET 10

Operating System

Windows

IDE / Test Runner

dotnet CLI (dotnet test / dotnet run)

Error Output / Stack Trace

Additional Context

No response

IDE-Specific Issue?

• I've confirmed this issue occurs when running via dotnet test or dotnet run, not just in my IDE