Remove pinning of pytest version

[NicolasHug]

Not sure it's fixed yet but let's see
Closes #8238

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/8243

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✅ You can merge normally! (18 Unrelated Failures)

As of commit 21800e1 with merge base 806dba6 ():

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• CMake / windows (windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job (gh)
  Process completed with exit code 2.
• Tests / unittests-extended / linux-job (gh)
  test/test_extended_models.py::TestHandleLegacyInterface::test_pretrained_deprecation[inception_v3_1]
• Tests / unittests-linux (3.10, linux.12xlarge, cpu) / linux-job (gh)
  RuntimeError: Command docker exec -t b4a69915e8dd006f1f8cf28f88538a4e0bf631d89e0efd0ce1ffbc52a29591fb /exec failed with exit code 2
• Tests / unittests-linux (3.11, linux.12xlarge, cpu) / linux-job (gh)
  RuntimeError: Command docker exec -t 65dcfb0f8371b81b105b2f8aca10e530a8041502676822d33fb064a31de5f1e4 /exec failed with exit code 2
• Tests / unittests-linux (3.8, linux.12xlarge, cpu) / linux-job (gh)
  RuntimeError: Command docker exec -t 2b623fd4afaa39f07b22ed4738fbb3ef5bdb405e843574a66e3652606801304d /exec failed with exit code 2
• Tests / unittests-linux (3.8, linux.g5.4xlarge.nvidia.gpu, cuda, 11.8) / linux-job (gh)
  RuntimeError: Command docker exec -t 6116a8c63451ab1c7bab6c438a346657e6998dbe50e838b75a9ad20a51c256c6 /exec failed with exit code 2
• Tests / unittests-linux (3.9, linux.12xlarge, cpu) / linux-job (gh)
  RuntimeError: Command docker exec -t 68a76dcad5da74c1d702800d1f7d8ae7990921a7f3064ccb36a518d3bbf13abc /exec failed with exit code 2
• Tests / unittests-macos (3.10, macos-12) / macos-job (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 2
• Tests / unittests-macos (3.11, macos-12) / macos-job (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 2
• Tests / unittests-macos (3.8, macos-12) / macos-job (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 2
• Tests / unittests-macos (3.8, macos-m1-12) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 2
• Tests / unittests-macos (3.9, macos-12) / macos-job (gh)
  RuntimeError: Command bash /Users/runner/work/_temp/exec_script failed with exit code 2
• Tests / unittests-windows (3.10, windows.4xlarge, cpu) / windows-job (gh)
  Process completed with exit code 2.
• Tests / unittests-windows (3.11, windows.4xlarge, cpu) / windows-job (gh)
  Process completed with exit code 2.
• Tests / unittests-windows (3.8, windows.4xlarge, cpu) / windows-job (gh)
  Process completed with exit code 2.
• Tests / unittests-windows (3.8, windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job (gh)
  Process completed with exit code 2.
• Tests / unittests-windows (3.9, windows.4xlarge, cpu) / windows-job (gh)
  Process completed with exit code 2.

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Build Windows Conda / pytorch/vision / conda-py3_8-cpu (gh)
  Process completed with exit code 1.

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