Update include path for t8_cmesh header

Author: sandro-elsweijer

test/mesh_handle/t8_gtest_custom_competence.cxx

@@ -32,7 +32,7 @@ along with t8code; if not, write to the Free Software Foundation, Inc.,
 #include <mesh_handle/mesh.hxx>
 #include <mesh_handle/element.hxx>
 #include <mesh_handle/competences.hxx>
-#include <t8_cmesh.h>
+#include <t8_cmesh/t8_cmesh.h>
 #include <t8_cmesh/t8_cmesh_examples.h>
 #include <t8_forest/t8_forest_general.h>
 #include <t8_schemes/t8_default/t8_default.hxx>