Bump dependency BenchmarkDotNet to 0.15.6 (#179)

| datasource | package         | from   | to     |
| ---------- | --------------- | ------ | ------ |
| nuget      | BenchmarkDotNet | 0.15.5 | 0.15.6 |

Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

Directory.Packages.props

@@ -3,6 +3,6 @@
     <GlobalPackageReference Include="StyleCop.Analyzers" Version="1.2.0-beta.556" PrivateAssets="All" />
   </ItemGroup>
   <ItemGroup>
-    <PackageVersion Include="BenchmarkDotNet" Version="0.15.5" />
+    <PackageVersion Include="BenchmarkDotNet" Version="0.15.6" />
   </ItemGroup>
 </Project>