test: use asynccontextmanager for FastAPI lifespan #1583

Job	Run time
find-tests	3s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_commit_wei...	13m 13s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_set_weight...	9m 43s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_transfer.py)	9m 29s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_commit_rev...	14m 7s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_dendrite.py)	14m 59s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_metagraph.py)	9m 3s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_root_set_w...	13m 17s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_neuron_cer...	9m 29s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_axon.py)	8m 21s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_liquid_alp...	8m 59s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_incentive.py)	11m 30s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_subtensor_...	8m 15s
	2h 10m 28s

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