accept percentages higher than 100% in --benchmark-compare-fail

[bentheiii]

for very chaotic benchmark, we sometimes want to accept changes of 100% or more, but pytest-benchmark doesn't accept this argument

>>> pytest tests/benchmark/*.py --benchmark-compare=0001 --benchmark-compare-fail=mean:100% --benchmark-compare-fail=median:100%
ERROR: usage: pytest [options] [file_or_dir] [file_or_dir] [...]
pytest: error: argument --benchmark-compare-fail: Could not parse value: 'mean:100%'.