Update AstraDBGraphVectorStore to match implementation of CassandraGraphVectorStore #321

Job	Run time
build	8s
cd libs/astradb / make test #3.9	29s
cd libs/astradb / make test #3.10	28s
cd libs/astradb / make test #3.11	24s
cd libs/astradb / make test #3.12	25s
cd libs/astradb / make lint #3.9	59s
cd libs/astradb / make integration_tests #3.12	14m 6s
cd libs/astradb / make lint #3.12	1m 54s
cd libs/astradb / poetry run pytest -m compile tests/integration_tests #3.9	16s
cd libs/astradb / poetry run pytest -m compile tests/integration_tests #3.10	20s
cd libs/astradb / poetry run pytest -m compile tests/integration_tests #3.11	16s
cd libs/astradb / poetry run pytest -m compile tests/integration_tests #3.12	19s
CI Success	1s
	20m 5s

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