Fix breaking changes from System.Memory in benchmarks

tests/ImageSharp.Benchmarks/Color/Bulk/PackFromVector4.cs

@@ -3,7 +3,7 @@ namespace SixLabors.ImageSharp.Benchmarks.Color.Bulk
 {
     using System.Numerics;
     using System.Runtime.CompilerServices;
-
+    using System.Runtime.InteropServices;
     using BenchmarkDotNet.Attributes;
 
     using SixLabors.ImageSharp.Memory;
@@ -37,8 +37,8 @@ namespace SixLabors.ImageSharp.Benchmarks.Color.Bulk
         [Benchmark(Baseline = true)]
         public void PerElement()
         {
-            ref Vector4 s = ref this.source.Span.DangerousGetPinnableReference();
-            ref TPixel d = ref this.destination.Span.DangerousGetPinnableReference();
+            ref Vector4 s = ref MemoryMarshal.GetReference(this.source.Span);
+            ref TPixel d = ref MemoryMarshal.GetReference(this.destination.Span);
             
             for (int i = 0; i < this.Count; i++)
             {

tests/ImageSharp.Benchmarks/ImageSharp.Benchmarks.csproj

@@ -17,7 +17,9 @@
   <ItemGroup>
     <PackageReference Include="BenchmarkDotNet" Version="0.10.12" />
     <PackageReference Include="Colourful" Version="1.1.2" />
-    <PackageReference Include="System.Drawing.Common" Version="4.5.0-preview2-26202-05" />
+    <PackageReference Include="System.Drawing.Common" Version="4.5.0-preview1-26216-02" />
+    <PackageReference Include="System.Memory" Version="4.5.0-preview1-26216-02" />
+    <PackageReference Include="System.Numerics.Vectors" Version="4.5.0-preview1-26216-02" />
   </ItemGroup>
 
   <ItemGroup>