[deps] Upgrade to pytest 9

[chrisvittal]

I was getting very strange warnings in my environment with pytest 7.x regarding unclosed files. Upgrading seems to have fixed it.

Security Assessment

• This change potentially impacts the Hail Batch instance as deployed by Broad Institute in GCP

Impact Rating

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• This change has no security impact

Impact Description

Dev dependency update

Appsec Review

• Required: The impact has been assessed and approved by appsec

[cjllanwarne]

If #15395 merges, the test batch for this PR would only have run the following steps:

[
    'check_hail',
    'check_pip_requirements',
    'check_services',
    'merge_code',
    'test_auth',
    'test_auth_copy_paste_login',
    'test_auth_copy_paste_login_timeout',
    'test_batch',
    'test_batch_docs',
    'test_batch_invariants',
    'test_batch_job_private_machines',
    'test_ci',
    'test_ci_unit',
    'test_hail_python',
    'test_hail_python_local_backend',
    'test_hail_python_service_backend_gcp',
    'test_hail_python_unchecked_allocator',
    'test_hailctl_batch',
    'test_hailtop_python',
    'test_hailtop_python_fs',
    'test_monitoring',
]