Avoid triggering memory leak in GPX driver (now fixed in GDAL per OSGeo/gdal@6c20fa9)

Author: rouault

msautotest/wxs/expected/wfsogr10_gpx.xml

@@ -1,7 +1,9 @@
+Content-Disposition: attachment; filename=result.gpx
 Content-Type: application/gpx+xml; streamed
 
 <?xml version="1.0"?>
 <gpx version="1.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:ogr="http://osgeo.org/gdal" xmlns="http://www.topografix.com/GPX/1/1" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd">
+<metadata><bounds minlat="90.00000000000000" minlon="180.00000000000000" maxlat="402556.25000000000000" maxlon="2589745.50000000000000"/></metadata>        
 <rte>
   <extensions>
     <ogr:FNODE_>613</ogr:FNODE_>

msautotest/wxs/wfs_ogr.map

@@ -145,7 +145,7 @@ OUTPUTFORMAT
   DRIVER "OGR/GPX"
   MIMETYPE "application/gpx+xml; streamed"
   FORMATOPTION "DSCO:GPX_USE_EXTENSIONS=YES"
-  FORMATOPTION "STORAGE=stream"
+  FORMATOPTION "STORAGE=memory"
   FORMATOPTION "FORM=simple"
   FORMATOPTION "FILENAME=result.gpx"
 END