Dipose XmlReaders in Microsoft.TestPlatform.Common.RunSettings (#5100)

It probably makes no impact, but the XmlReaders are declared as
IDisposable, so we should Dispose() them when done using them.

Co-authored-by: Jakub Jareš <[email protected]>

src/Microsoft.TestPlatform.Common/RunSettings.cs

@@ -80,7 +80,7 @@ public void LoadSettingsXml(string settings)
         }
 
         using var stringReader = new StringReader(settings);
-        var reader = XmlReader.Create(stringReader, XmlRunSettingsUtilities.ReaderSettings);
+        using var reader = XmlReader.Create(stringReader, XmlRunSettingsUtilities.ReaderSettings);
         ValidateAndSaveSettings(reader);
     }
 
@@ -91,7 +91,7 @@ public void LoadSettingsXml(string settings)
     public void InitializeSettingsProviders(string settings)
     {
         using var stringReader = new StringReader(settings);
-        var reader = XmlReader.Create(stringReader, XmlRunSettingsUtilities.ReaderSettings);
+        using var reader = XmlReader.Create(stringReader, XmlRunSettingsUtilities.ReaderSettings);
         ReadRunSettings(reader);
     }