build: only run db backup for odk if CENTRAL_DB_HOST is not default #1224

Job	Run time
pytest / check-img-cache	10s
frontend-tests / Run Frontend Tests	27s
pytest / test-img-build	0s
pytest / run-tests	2m 47s
frontend-build / build-image	1m 30s
frontend-build / scan-image	20s
smoke-test-frontend	1m 0s
backend-build / build-image	2m 16s
backend-build / scan-image	46s
smoke-test-backend	1m 6s
deploy-containers / remote-deploy	1m 22s
	11m 44s

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