Fix spelling and API doc

python/core/geometry/qgsgeometry.sip

@@ -755,6 +755,7 @@ class QgsGeometry
      * In case of full or partial dimensional collapses, the output geometry may be a collection
      * of lower-to-equal dimension geometries or a geometry of lower dimension.
      * Single polygons may become multi-geometries in case of self-intersections.
+     * It preserves Z values, but M values will be dropped.
      * @return new valid QgsGeometry or null geometry on error
      * @note added in QGIS 3.0
      */

src/core/geometry/qgsgeometry.h

@@ -810,6 +810,7 @@ class CORE_EXPORT QgsGeometry
      * In case of full or partial dimensional collapses, the output geometry may be a collection
      * of lower-to-equal dimension geometries or a geometry of lower dimension.
      * Single polygons may become multi-geometries in case of self-intersections.
+     * It preserves Z values, but M values will be dropped.
      * @return new valid QgsGeometry or null geometry on error
      * @note added in QGIS 3.0
      */

src/core/geometry/qgsgeometrymakevalid.cpp

@@ -494,7 +494,7 @@ static GEOSGeometry* LWGEOM_GEOS_makeValidPolygon( const GEOSGeometry* gin, QStr
   }
 
   // NOTE: the noding process may drop lines collapsing to points.
-  //       We want to retrive any of those
+  //       We want to retrieve any of those
   {
     GEOSGeometry* pi;
     GEOSGeometry* po;