CONTRIBUTING.md: Remove trailing whitespaces #1089

Job	Run time
onnx / linux-job	5m 43s
unittests-extended / linux-job	17m 37s
unittests-macos (3.10, macos-12) / macos-job	2m 48s
unittests-macos (3.11, macos-12) / macos-job	2m 21s
unittests-macos (3.8, macos-12) / macos-job	2m 34s
unittests-macos (3.8, macos-m1-12) / macos-job	1m 28s
unittests-macos (3.9, macos-12) / macos-job	3m 7s
unittests-linux (3.10, linux.12xlarge, cpu) / linux-job	28m 46s
unittests-linux (3.11, linux.12xlarge, cpu) / linux-job	23m 56s
unittests-linux (3.8, linux.12xlarge, cpu) / linux-job	28m 34s
unittests-linux (3.8, linux.g5.4xlarge.nvidia.gpu, cuda, 11.8) / linux-job	1m 1s
unittests-linux (3.9, linux.12xlarge, cpu) / linux-job	27m 56s
unittests-windows (3.10, windows.4xlarge, cpu) / windows-job	1m 29s
unittests-windows (3.11, windows.4xlarge, cpu) / windows-job	1m 47s
unittests-windows (3.8, windows.4xlarge, cpu) / windows-job	1m 32s
unittests-windows (3.8, windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job	25m 9s
unittests-windows (3.9, windows.4xlarge, cpu) / windows-job	1m 54s
	2h 57m 42s

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