update dependency benchmarkdotnet to 0.15.0 (#351)

Author: renovate[bot]

tests/Prometheus.Client.Benchmarks.Comparison/Prometheus.Client.Benchmarks.Comparison.csproj

@@ -6,7 +6,7 @@
     <NoWarn>$(NoWarn);SA1133</NoWarn>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.14.0" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.15.0" />
     <PackageReference Include="prometheus-net" Version="8.2.1" />
   </ItemGroup>
   <ItemGroup>

tests/Prometheus.Client.Benchmarks/Prometheus.Client.Benchmarks.csproj

@@ -6,7 +6,7 @@
     <OutputType>Exe</OutputType>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.14.0" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.15.0" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\src\Prometheus.Client\Prometheus.Client.csproj" />