C#: Fix cleanup logic in dependency manager

Author: tamasvajk

csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyManager.cs

@@ -564,9 +564,12 @@ private void AnalyseProject(FileInfo project)
 
         public void Dispose()
         {
-            tempWorkingDirectory?.Dispose();
-            diagnosticsWriter?.Dispose();
             nugetPackageRestorer?.Dispose();
+            if (cleanupTempWorkingDirectory)
+            {
+                tempWorkingDirectory?.Dispose();
+            }
+            diagnosticsWriter?.Dispose();
         }
     }
 }