update dependency system.valuetuple to 4.6.1 (#349)

Author: renovate[bot]

src/Prometheus.Client.Abstractions/Prometheus.Client.Abstractions.csproj

@@ -6,6 +6,6 @@
     <RepositoryUrl>https://github.com/prom-client-net/prom-client</RepositoryUrl>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'net462'">
-    <PackageReference Include="System.ValueTuple" Version="4.6.0" />
+    <PackageReference Include="System.ValueTuple" Version="4.6.1" />
   </ItemGroup>
 </Project>