Started adding tests on the for the project rewriter

src/Credfeto.DotNet.Repo.Tools.CleanUp/Services/ProjectXmlRewriter.cs

@@ -49,7 +49,7 @@ public void ReOrderPropertyGroups(XmlDocument projectDocument, string filename)
             Dictionary<string, XmlNode> orderedChildren = new(StringComparer.Ordinal);
             bool replace = true;
 
-            foreach (XmlNode child in children)
+            foreach (XmlElement child in children)
             {
                 string name = child.Name;