291 Added backwards compatibility

[Marvin-Brouwer]

Fixes #291.

To test this I referenced this project directly, in a multi target project, like so:

	<ItemGroup Condition="'$(TargetFramework)' == 'net7.0'">
		<Reference Include="Ardalis.GuardClauses">
			<HintPath>..\..\..\GuardClauses\src\GuardClauses\bin\Release\net7.0\Ardalis.GuardClauses.dll</HintPath>
		</Reference>
	</ItemGroup>
	<ItemGroup Condition="'$(TargetFramework)' == 'net6.0'">
		<Reference Include="Ardalis.GuardClauses">
			<HintPath>..\..\..\GuardClauses\src\GuardClauses\bin\Release\netstandard2.1\Ardalis.GuardClauses.dll</HintPath>
		</Reference>
	</ItemGroup>
	<ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.1'">
		<Reference Include="Ardalis.GuardClauses">
			<HintPath>..\..\..\GuardClauses\src\GuardClauses\bin\Release\netstandard2.1\Ardalis.GuardClauses.dll</HintPath>
		</Reference>
	</ItemGroup>
	<ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
		<Reference Include="Ardalis.GuardClauses">
			<HintPath>..\..\..\GuardClauses\src\GuardClauses\bin\Release\netstandard2.0\Ardalis.GuardClauses.dll</HintPath>
		</Reference>
	</ItemGroup>

I changed one of my unit-test that validated a Guard.Against.Null(...); into net6.0 and stepped into a test. It did automatically resolve the parameterName in Lang version 10.

Feel free to validate this locally before approving.

[ardalis]

Cool, thanks! I'll try to make time to try this out soon. Pretty overwhelmed at the moment.