fix: use sln instead of slnx to fix pipeline issue

Author: philasmar

Diff for: buildtools/build.proj

@@ -195,7 +195,7 @@
     </Target>
     <Target Name="testtoolv2-tests" DependsOnTargets="testtoolv2-unit-tests;testtoolv2-integ-tests"></Target>
     <Target Name="testtoolv2-build">
-        <Exec Command="dotnet build -c $(Configuration) Amazon.Lambda.TestTool.slnx" WorkingDirectory="..\Tools\LambdaTestTool-v2" ConsoleToMSBuild="true"/>
+        <Exec Command="dotnet build -c $(Configuration) Amazon.Lambda.TestTool.sln" WorkingDirectory="..\Tools\LambdaTestTool-v2" ConsoleToMSBuild="true"/>
     </Target>
     <Target Name="testtoolv2-unit-tests" DependsOnTargets="testtoolv2-build">
         <Exec Command="dotnet test -c $(Configuration) --logger &quot;console;verbosity=detailed&quot; 2>&amp;1"