test: use asynccontextmanager for FastAPI lifespan #1593

Job	Run time
find-tests	5s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_axon.py)	9m 47s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_root_set_w...	9m 44s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_incentive.py)	11m 28s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_transfer.py)	8m 30s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_metagraph.py)	9m 1s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_set_weight...	9m 19s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_liquid_alp...	8m 44s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_subtensor_...	12m 37s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_commit_wei...	15m 50s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_dendrite.py)	14m 25s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_commit_rev...	17m 54s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_neuron_cer...	12m 36s
	2h 20m 0s

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