feat(csharp): Enable NuGet publishing for Apache.Arrow.Adbc.Testing (#3907)

Enable NuGet publishing for Apache.Arrow.Adbc.Testing to eliminate the
need for submodules in the driver test projects.

Co-authored-by: David Coe <>

Author: davidhcoe

csharp/test/Apache.Arrow.Adbc.Tests/Apache.Arrow.Adbc.Testing.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <TargetFrameworks Condition="'$(IsWindows)'=='true'">net8.0;net472</TargetFrameworks>
     <TargetFrameworks Condition="'$(TargetFrameworks)'==''">net8.0</TargetFrameworks>
-    <IsPackable>false</IsPackable>
+    <IsPackable>true</IsPackable>
     <IsTestProject>true</IsTestProject>
     <ProcessArchitecture>$([System.Runtime.InteropServices.RuntimeInformation]::ProcessArchitecture.ToString().ToLowerInvariant())</ProcessArchitecture>
   </PropertyGroup>