Bump Verify.Xunit: 20.3.2->20.8.2

Author: AndreyAkinshin

tests/BenchmarkDotNet.Tests/BenchmarkDotNet.Tests.csproj

@@ -16,7 +16,8 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.6.2" />
-    <PackageReference Include="Verify.Xunit" Version="20.3.2" />
+    <!-- We use Verify.Xunit v20.8.2 because it's the latest version with net461 support -->
+    <PackageReference Include="Verify.Xunit" Version="[20.8.2]" />
     <PackageReference Include="xunit" Version="2.6.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.4">
       <PrivateAssets>all</PrivateAssets>