Fix preprocessor directives in EF Core project to account for net6.0

[fiseni]

Some of the ORM features are not available in EF Core 3, so we've been using preprocessor directives. The condition was fine, but now that we added additional TFM net6.0, they're excluded from it as well.

	public SpecificationEvaluator(bool cacheEnabled = false)
	{
		this.evaluators.AddRange(new IEvaluator[]
		{
			WhereEvaluator.Instance,
			SearchEvaluator.Instance,
			cacheEnabled ? IncludeEvaluator.Cached : IncludeEvaluator.Default,
			OrderEvaluator.Instance,
			PaginationEvaluator.Instance,
			AsNoTrackingEvaluator.Instance,
			IgnoreQueryFiltersEvaluator.Instance,
#if NETSTANDARD2_1
			AsSplitQueryEvaluator.Instance,
			AsNoTrackingWithIdentityResolutionEvaluator.Instance
#endif
		});
	}

So, instead of #if NETSTANDARD2_1, we should use negation #if !NETSTANDARD2_0.