Bump Nerdbank.GitVersioning from 3.1.68 to 3.1.71 in /Rx.NET/Source

Bumps [Nerdbank.GitVersioning](https://github.com/dotnet/Nerdbank.GitVersioning) from 3.1.68 to 3.1.71.
- [Release notes](https://github.com/dotnet/Nerdbank.GitVersioning/releases)
- [Commits](https://github.com/dotnet/Nerdbank.GitVersioning/compare/v3.1.68...v3.1.71)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Rx.NET/Source/Directory.build.props

@@ -25,7 +25,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All"/>
-    <PackageReference Include="Nerdbank.GitVersioning" Version="3.1.68" PrivateAssets="all" />
+    <PackageReference Include="Nerdbank.GitVersioning" Version="3.1.71" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(IsTestProject)' == 'true'">