Fix a failing unit test [#32813]

This should fix a unit test that is currently failing like:
```
1) JRegistryFormatXMLTest::testObjectToString
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
 '<?xml version="1.0"?>
-<registry><node name="foo" type="string">bar</node><node name="quoted" type="string">"stringwithquotes"</node><node name="booleantrue" type="boolean">1</node><node name="booleanfalse" type="boolean"></node><node name="numericint" type="integer">42</node><node name="numericfloat" type="double">3.1415</node><node name="section" type="object"><node name="key" type="string">value</node></node><node name="array" type="array"><node name="nestedarray" type="array"><node name="test1" type="string">value1</node></node></node></registry>
+<registry><node name="foo" type="string">bar</node><node name="quoted" type="string">"stringwithquotes"</node><node name="booleantrue" type="boolean">1</node><node name="booleanfalse" type="boolean"/><node name="numericint" type="integer">42</node><node name="numericfloat" type="double">3.1415</node><node name="section" type="object"><node name="key" type="string">value</node></node><node name="array" type="array"><node name="nestedarray" type="array"><node name="test1" type="string">value1</node></node></node></registry>
 '
```

Ref: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=32813&start=0