Bump BenchmarkDotNet from 0.13.7 to 0.13.8

Bumps [BenchmarkDotNet](https://github.com/dotnet/BenchmarkDotNet) from 0.13.7 to 0.13.8.
- [Release notes](https://github.com/dotnet/BenchmarkDotNet/releases)
- [Commits](dotnet/BenchmarkDotNet@v0.13.7...v0.13.8)

---
updated-dependencies:
- dependency-name: BenchmarkDotNet
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

benchmarks/RestSharp.Benchmarks/RestSharp.Benchmarks.csproj

@@ -9,7 +9,7 @@
 
     <ItemGroup>
         <PackageReference Include="AutoFixture" Version="4.18.0" />
-        <PackageReference Include="BenchmarkDotNet" Version="0.13.7" />
+        <PackageReference Include="BenchmarkDotNet" Version="0.13.8" />
         <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.6.0" />
     </ItemGroup>
     <ItemGroup>