Fix MethodDataSource example in property injection documentation

[Copilot]

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• If this is a new feature or piece of functionality, have you started a discussion and gotten agreement on it?
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Fixes #3884

Description

The property injection docs showed MethodDataSource returning IEnumerable<string>, which triggers TUnit0001 error. For property injection, the method must return the property's type directly—not an enumerable.

Before (incorrect):

[MethodDataSource(nameof(GetMethodData))]
public required string Property2 { get; init; }

public static IEnumerable<string> GetMethodData()
{
    yield return "method_data_1";
    yield return "method_data_2";
}

After (matches TUnit.TestProject/PropertySetterTests.cs):

[MethodDataSource(nameof(GetMethodData))]
public required string Property2 { get; init; }

public static string GetMethodData() => "method_data_value";

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Doc] Basic Property Injection Examples TUnit0001 Error</issue_title>
<issue_description>The code in https://tunit.dev/docs/test-lifecycle/property-injection#basic-property-injection-examples got an error in the version 1.2.11.

I Got the error TUnit0001: Attribute argument types 'System.Collections.Generic.IEnumerable<string>' don't match method parameter types 'string' in the line [MethodDataSource(nameof(GetMethodData))]

However in the code about this feature, is like this in the github:

TUnit/TUnit.TestProject/PropertySetterTests.cs

Lines 15 to 16 in 4c62596

	[MethodDataSource(nameof(MethodData))]
	public required string Property2 { get; init; }

TUnit/TUnit.TestProject/PropertySetterTests.cs

Line 126 in 4c62596

public static string MethodData() => "2";

Could you please update the document?

BTW, can we get the feature like the document?</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Doc] Basic Property Injection Examples TUnit0001 Error #3884

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