Reference GitHub.Extensions in UI unit tests.

Author: grokys

test/GitHub.UI.UnitTests/GitHub.UI.UnitTests.csproj

@@ -69,6 +69,10 @@
       <Project>{9aea02db-02b5-409c-b0ca-115d05331a6b}</Project>
       <Name>GitHub.Exports</Name>
     </ProjectReference>
+    <ProjectReference Include="..\..\src\GitHub.Extensions\GitHub.Extensions.csproj">
+      <Project>{6afe2e2d-6db0-4430-a2ea-f5f5388d2f78}</Project>
+      <Name>GitHub.Extensions</Name>
+    </ProjectReference>
     <ProjectReference Include="..\..\src\GitHub.UI\GitHub.UI.csproj">
       <Project>{346384dd-2445-4a28-af22-b45f3957bd89}</Project>
       <Name>GitHub.UI</Name>