Improved test coverage in decimal_to_fraction.py (#12608)

* Imporved test coverage in  decimal_to_fraction.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Update decimal_to_fraction.py

* Update decimal_to_fraction.py

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Maxim Smolskiy <mithridatus@mail.ru>