only run pyav backend tests for VideoReader if av is available

[pmeier]

No description provided.

[pytorch-bot]

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❌ 27 New Failures

As of commit d49aeb3:

NEW FAILURES - The following jobs have failed:

• build / linux-job (gh)
• c-source / linux-job (gh)
• linux (linux.g5.4xlarge.nvidia.gpu, cuda, 11.8) / linux-job (gh)
• macos (macos-12) / macos-job (gh)
• onnx / linux-job (gh)
• python-source-and-configs / linux-job (gh)
• python-types / linux-job (gh)
• unittests-extended / linux-job (gh)
• unittests-linux (3.10, linux.12xlarge, cpu) / linux-job (gh)
• unittests-linux (3.11, linux.12xlarge, cpu) / linux-job (gh)
• unittests-linux (3.8, linux.12xlarge, cpu) / linux-job (gh)
• unittests-linux (3.8, linux.g5.4xlarge.nvidia.gpu, cuda, 11.8) / linux-job (gh)
• unittests-linux (3.9, linux.12xlarge, cpu) / linux-job (gh)
• unittests-macos (3.10, macos-12) / macos-job (gh)
• unittests-macos (3.11, macos-12) / macos-job (gh)
• unittests-macos (3.8, macos-12) / macos-job (gh)
• unittests-macos (3.8, macos-m1-12) / macos-job (gh)
• unittests-macos (3.9, macos-12) / macos-job (gh)
• unittests-prototype (3.11, linux.12xlarge, cpu) / linux-job (gh)
• unittests-prototype (3.8, linux.12xlarge, cpu) / linux-job (gh)
• unittests-prototype (3.8, linux.g5.4xlarge.nvidia.gpu, cuda, 11.8) / linux-job (gh)
• unittests-prototype (3.9, linux.12xlarge, cpu) / linux-job (gh)
• unittests-windows (3.10, windows.4xlarge, cpu) / windows-job (gh)
• unittests-windows (3.11, windows.4xlarge, cpu) / windows-job (gh)
• unittests-windows (3.8, windows.4xlarge, cpu) / windows-job (gh)
• unittests-windows (3.9, windows.4xlarge, cpu) / windows-job (gh)
• windows (windows.4xlarge, cpu) / windows-job (gh)

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[NicolasHug]

Thanks Philip, as discussed offline these tests have been skipped forever already.

LGTM if green, ideally with a big disclaimer at the top of this file as a comment like

# WARNING: these tests have been skipped forever on the CI because the video ops are never properly available. This is bad, but things have been in a terrible state for a long time already as we write this comment, and we'll hopefully be able to get rid of this all soon. 

I don't mind committing it if you prefer

[pmeier]

I don't mind committing it if you prefer

Please send a commit then. I'll leave merging the PR up to you.

[github-actions]

Hey @NicolasHug!

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