MINOR: [C#] Bump Grpc.Net.ClientFactory from 2.70.0 to 2.71.0 in /csharp

Bumps [Grpc.Net.ClientFactory](https://github.com/grpc/grpc-dotnet) from 2.70.0 to 2.71.0.
- [Release notes](https://github.com/grpc/grpc-dotnet/releases)
- [Changelog](https://github.com/grpc/grpc-dotnet/blob/master/doc/release_process.md)
- [Commits](grpc/grpc-dotnet@v2.70.0...v2.71.0)

---
updated-dependencies:
- dependency-name: Grpc.Net.ClientFactory
  dependency-version: 2.71.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

csharp/test/Apache.Arrow.Flight.Tests/Apache.Arrow.Flight.Tests.csproj

@@ -6,7 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Grpc.Net.ClientFactory" Version="2.70.0" />
+    <PackageReference Include="Grpc.Net.ClientFactory" Version="2.71.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
     <PackageReference Include="xunit" Version="2.9.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="3.0.2" />