Exec PrepareTests.dll instead of 'dotnet run' on project (#50006)

eng/prepare-tests.ps1

@@ -11,7 +11,7 @@ try {
   $dotnet = Ensure-DotnetSdk
   # permissions issues make this a pain to do in PrepareTests itself.
   Remove-Item -Recurse -Force "$RepoRoot\artifacts\testPayload" -ErrorAction SilentlyContinue
-  Exec-Console $dotnet "run --project src\Tools\PrepareTests\PrepareTests.csproj $RepoRoot $RepoRoot\artifacts\testPayload"
+  Exec-Console $dotnet "$RepoRoot\artifacts\bin\PrepareTests\$configuration\net5.0\PrepareTests.dll $RepoRoot $RepoRoot\artifacts\testPayload"
   exit 0
 }
 catch {

eng/prepare-tests.sh

@@ -28,4 +28,4 @@ InitializeDotNetCli true
 # permissions issues make this a pain to do in PrepareTests itself.
 rm -rf "$repo_root/artifacts/testPayload"
 
-dotnet run --project src/Tools/PrepareTests/PrepareTests.csproj "$repo_root" "$repo_root/artifacts/testPayload"
+dotnet "$repo_root/artifacts/bin/PrepareTests/Debug/net5.0/PrepareTests.dll" "$repo_root" "$repo_root/artifacts/testPayload"