[RELEASE-ONLY CHANGES] [Cherry-pick for 0.17] CI fix - Use pytest<8 in unittest jobs

[NicolasHug]

Cherry pick of #8239. We need to use pytest7 as pytest8 (released this weekend) is causing issues.

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/8240

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✅ You can merge normally! (1 Unrelated Failure)

As of commit cac8b38 with merge base e12d200 ():

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• CMake / windows (windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job (gh)
  The process cannot access the file 'C:\actions-runner\_work\_actions\pytorch\pytorch\main\docs\source\_static\img\pipeline_parallelism' because it is being used by another process.

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[pmeier]

Thanks!