[GML] asGml3() creates invalid GML for CurvePolygon

[pathmapper]

What is the bug or the crash?

asGml3() creates invalid GML for CurvePolygon in terms of XML schema validation:

exterior expects child elements of type AbstractRing (e.g. Ring or LinearRing) not CompositeCurve.

In QGIS Python console:

wkt_geom = 'CURVEPOLYGON (COMPOUNDCURVE ((0 -1,0 1),CIRCULARSTRING (0 1,1 0,0 -1)))'

geometry = QgsGeometry.fromWkt(wkt_geom)

doc = QDomDocument()
gml_geometry = geometry.constGet().asGml3(doc, 0)
doc.appendChild(gml_geometry)

print(doc.toString(2))

results in:

Steps to reproduce the issue

see above

Versions

QGIS version	3.37.0-Master	QGIS code revision	8189860
Qt version	5.15.3
Python version	3.10.12
GDAL/OGR version	3.9.0dev-18f9ed2b7c
PROJ version	8.2.1
EPSG Registry database version	v10.041 (2021-12-03)
GEOS version	3.10.2-CAPI-1.16.0
SQLite version	3.37.2
PDAL version	2.3.0
PostgreSQL client version	14.11 (Ubuntu 14.11-0ubuntu0.22.04.1)
SpatiaLite version	5.0.1
QWT version	6.1.4
QScintilla2 version	2.11.6
OS version	Ubuntu 22.04.4 LTS
Active Python plugins
grassprovider	2.12.99
MetaSearch	0.3.6
processing	2.12.99
db_manager	0.1.20

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

A similar issue existed in GDAL OSGeo/gdal#7294 and was fixed by @rouault in OSGeo/gdal#7296.