Use hexfloat for threshold OpInfo tests (#85676)
0.123 isn't exactly representable as a floating point value, and so
the threshold will move marginally depending on the data type where
the computation is performed. This leads to a rare flake in tests
comparing against a reference implementation.
Instead, this chooses a threshold which is exactly representable as a
bfloat16 value and thus has the same value for all data types.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85676
Approved by: https://github.com/ngimel
