Revert "Drop NuGet restore"

This reverts commit 5c7a0d05f077755943ec66e6a82db890a24cd056.

azure-pipelines.yml

@@ -9,6 +9,9 @@ steps:
     msbuild /t:Restore Terminal.sln
   displayName: Restore dependencies
 
+- script: |
+    nuget restore
+  displayName: Nuget restore
 
 - script: |
     if echo $BUILD_SOURCEBRANCH | grep /release/; then perl -pi -e "s/PackageVersion>.*</PackageVersion>${BUILD_SOURCEBRANCHNAME}</" Terminal.Gui/Terminal.Gui.csproj; fi