[Misc] Add graphbolt dir for test script. (#6391)

Co-authored-by: Ubuntu <ubuntu@ip-172-31-28-63.ap-northeast-1.compute.internal>
Co-authored-by: LastWhisper <whuwkl@gmail.com>

script/run_pytest.sh

@@ -56,7 +56,7 @@ shift $(($OPTIND-1))
 
 export DGLBACKEND=pytorch
 export DGL_LIBRARY_PATH=${DGL_HOME}/build
-export PYTHONPATH=${DGL_HOME}/python:${DGL_HOME}/tests:$PYTHONPATH
+export PYTHONPATH=${DGL_HOME}/python:${DGL_HOME}/tests:${DGL_HOME}/tests/python/pytorch/graphbolt:$PYTHONPATH
 export DGLTESTDEV=${device}
 export DGL_DOWNLOAD_DIR=${DGL_HOME}/_download