Remove pinning of pytest version #2931

Job	Run time
onnx / linux-job	4m 48s
unittests-extended / linux-job	17m 29s
unittests-linux (3.10, linux.12xlarge, cpu) / linux-job	23m 5s
unittests-linux (3.11, linux.12xlarge, cpu) / linux-job	21m 17s
unittests-linux (3.12, linux.12xlarge, cpu) / linux-job	22m 12s
unittests-linux (3.8, linux.12xlarge, cpu) / linux-job	23m 30s
unittests-linux (3.8, linux.g5.4xlarge.nvidia.gpu, cuda, 11.8) / linux-job	20m 46s
unittests-linux (3.9, linux.12xlarge, cpu) / linux-job	22m 56s
unittests-macos (3.10, macos-m1-stable) / macos-job	27m 10s
unittests-macos (3.11, macos-m1-stable) / macos-job	20m 51s
unittests-macos (3.12, macos-m1-stable) / macos-job	23m 25s
unittests-macos (3.8, macos-m1-stable) / macos-job	24m 14s
unittests-macos (3.9, macos-m1-stable) / macos-job	24m 15s
unittests-windows (3.10, windows.4xlarge, cpu) / windows-job	1h 0m 2s
unittests-windows (3.11, windows.4xlarge, cpu) / windows-job	53m 30s
unittests-windows (3.12, windows.4xlarge, cpu) / windows-job	57m 33s
unittests-windows (3.8, windows.4xlarge, cpu) / windows-job	56m 51s
unittests-windows (3.9, windows.4xlarge, cpu) / windows-job	54m 57s
unittests-windows (3.8, windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job	23m 27s
	9h 42m 18s

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