test: use asynccontextmanager for FastAPI lifespan #1579

Job	Run time
find-tests	3s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_axon.py)	12m 16s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_root_set_w...	10m 8s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_incentive.py)	17m 12s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_transfer.py)	10m 55s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_metagraph.py)	11m 24s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_set_weight...	10m 56s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_liquid_alp...	10m 41s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_subtensor_...	10m 56s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_commit_wei...	12m 35s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_dendrite.py)	10m 46s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_commit_rev...	14m 30s
run (nightly-2024-03-05, x86_64-unknown-linux-gnu, ubuntu-latest, tests/e2e_tests/test_neuron_cer...	9m 4s
	2h 21m 26s

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