qgselevationprofilecanvas: Remove the current job on clear

When the canvas is cleared, the current job is not deleted. Therefore,
snapping is still active.

This issue is fixed by calling `cancelJobs` on clear.

Closes: #50766

src/gui/elevation/qgselevationprofilecanvas.cpp

@@ -1428,7 +1428,7 @@ QVector<QgsProfileIdentifyResults> QgsElevationProfileCanvas::identify( const QR
 void QgsElevationProfileCanvas::clear()
 {
   setProfileCurve( nullptr );
-  mPlotItem->setRenderer( nullptr );
+  cancelJobs();
   mPlotItem->updatePlot();
 }