TST: fix ujson tests failures on 32-bit

As pointed out by @lodagro [here](https://github.com/pydata/pandas/commit/a8d15bd4c6dae2c65ed4aa4b2f76c029b6358113#commitcomment-3521549) and [here](https://github.com/pydata/pandas/commit/a8d15bd4c6dae2c65ed4aa4b2f76c029b6358113#commitcomment-3521581) some of the ujson tests fail on 32-bit due to precision errors.

The changes below amend the tests so they pass.