ci(deps): bump actions/cache from 5 to 6 - #180

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/setup-dotnet@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

'CancellationTokenSource.Cancel()' synchronously blocks. Await 'CancellationTokenSource.CancelAsync()' instead. (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1849)

Prefer the generic overload 'System.Enum.IsDefined<TEnum>(TEnum)' instead of 'System.Enum.IsDefined(System.Type, object)' (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2263)

Prefer the generic overload 'System.Enum.IsDefined<TEnum>(TEnum)' instead of 'System.Enum.IsDefined(System.Type, object)' (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2263)

Prefer the generic overload 'System.Enum.IsDefined<TEnum>(TEnum)' instead of 'System.Enum.IsDefined(System.Type, object)' (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2263)

Prefer the generic overload 'System.Enum.IsDefined<TEnum>(TEnum)' instead of 'System.Enum.IsDefined(System.Type, object)' (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2263)

Null should not be used for type parameter 'invalidPath' of type 'string'. Use a non-null value, or convert the parameter to a nullable type. (https://xunit.net/xunit.analyzers/rules/xUnit1012)

Null should not be used for type parameter 'invalidPath' of type 'string'. Use a non-null value, or convert the parameter to a nullable type. (https://xunit.net/xunit.analyzers/rules/xUnit1012)

The field 'NuGetPluginLoaderTests._testPackageId' is assigned but its value is never used

Field 'PluginSystemTests._pluginSystem' is never assigned to, and will always have its default value null