Fixed mypy issue in VideoClips #1758

Job	Run time
onnx / linux-job	5m 7s
unittests-extended / linux-job	8m 59s
unittests-linux (3.10, linux.12xlarge, cpu) / linux-job	7m 5s
unittests-linux (3.11, linux.12xlarge, cpu) / linux-job	7m 4s
unittests-linux (3.8, linux.12xlarge, cpu) / linux-job	6m 13s
unittests-linux (3.8, linux.g5.4xlarge.nvidia.gpu, cuda, 11.8) / linux-job	8m 30s
unittests-linux (3.9, linux.12xlarge, cpu) / linux-job	6m 4s
unittests-macos (3.10, macos-12) / macos-job	8m 17s
unittests-macos (3.11, macos-12) / macos-job	8m 14s
unittests-macos (3.8, macos-12) / macos-job	8m 16s
unittests-macos (3.8, macos-m1-12) / macos-job	8m 17s
unittests-macos (3.9, macos-12) / macos-job	8m 18s
unittests-windows (3.11, windows.4xlarge, cpu) / windows-job	2s
unittests-windows (3.10, windows.4xlarge, cpu) / windows-job	3s
unittests-windows (3.8, windows.4xlarge, cpu) / windows-job	16s
unittests-windows (3.8, windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job	8m 15s
unittests-windows (3.9, windows.4xlarge, cpu) / windows-job	12s
	1h 39m 12s

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