Fix clazy mixed const/non-const iterator warnings

Author: nyalldawson

src/analysis/vector/geometry_checker/qgsgeometrycheckerutils.cpp

@@ -99,7 +99,7 @@ namespace QgsGeometryCheckerUtils
       }
       if ( mParent->mGeometryTypes.contains( mParent->mFeaturePools[*mLayerIt]->getLayer()->geometryType() ) )
       {
-        mFeatureIt = mParent->mFeatureIds[*mLayerIt].begin();
+        mFeatureIt = mParent->mFeatureIds[*mLayerIt].constBegin();
         return true;
       }
       ++mLayerIt;