Created attachment 38224 [details]
You can use this pptx to reproduce

## Issue

The POIXMLPropertiesTextExtractor::getCorePropertiesText() method returns a duplicate key "Category".

Check this line of Code: https://github.com/apache/poi/blob/b6aee1ef6d3e92a28ffd4b5c03e677b63b43747f/poi-ooxml/src/main/java/org/apache/poi/ooxml/extractor/POIXMLPropertiesTextExtractor.java#L115


## To reproduce: 

1. Create a new pptx file in Powerpoint. 
2. Add a category metadata to the pptx in Powerpoint (File > Properties > Summary > Enter a value in Category)
3. Read the ppt in POI and print the metadata as such -> 
 ```

        FileInputStream stream = new FileInputStream(new File("myfile.pptx"));

        XMLSlideShow doc = new XMLSlideShow(stream);
        SlideShowExtractor<XSLFShape, XSLFTextParagraph> extractor = new SlideShowExtractor<>(doc);
        String metaText = extractor.getMetadataTextExtractor().getText();
        System.out.println(metaText);
 ```
4. Observe the duplicate "Category" value