Use File.OpenRead when loading tool configuration (7.0.2xx backport) (#29549)

Author: SeanKilleen

src/Cli/dotnet/ToolPackage/ToolConfigurationDeserializer.cs

@@ -25,7 +25,7 @@ public static ToolConfiguration Deserialize(string pathToXml)
 
             try
             {
-                using (var fs = new FileStream(pathToXml, FileMode.Open))
+                using (var fs = File.OpenRead(pathToXml))
                 {
                     var reader = XmlReader.Create(fs);
                     dotNetCliTool = (DotNetCliTool)serializer.Deserialize(reader);