Handle NaN in array_with_unit_to_datetime
closes https://github.com/pandas-dev/pandas/issues/48610

Missing values in arrays can either be NaT (for integer types) or NaN (for
floating types).  Make sure to also handle the latter.  This fixes all
failing tests.

Does this fix an existing Github issue? Would need tests as well The existing tests already cover it perfectly.
 You mentioned 

> This fixes all failing tests

What tests were failing?  https://build.opensuse.org/package/live_build_log/openSUSE:Factory:RISCV/python-pandas:test-py310/standard/riscv64

=========================== short test summary info ============================
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_convert_dates_infer[trade_time]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_convert_dates_infer[date]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_convert_dates_infer[datetime]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_convert_dates_infer[sold_at]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_convert_dates_infer[modified]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_convert_dates_infer[timestamp]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_convert_dates_infer[timestamps]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_date_unit[s]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_date_unit[ms]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_date_unit[us]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_to_json_from_json_columns_dtypes[split]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_to_json_from_json_columns_dtypes[records]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_to_json_from_json_columns_dtypes[index]
FAILED pandas/tests/io/json/test_pandas.py::TestPandasContainer::test_to_json_from_json_columns_dtypes[columns]
FAILED pandas/tests/tools/test_to_datetime.py::TestToDatetimeUnit::test_to_datetime_unit_with_nulls[nan]
= 15 failed, 143030 passed, 9020 skipped, 1047 xfailed, 6 xpassed, 18 warnings in 16656.29s (4:37:36) =
 So this is related to https://github.com/pandas-dev/pandas/issues/48610? Yes.
 $ python3
Python 3.10.7 (main, Sep 11 2022, 08:41:56) [GCC] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np
>>> np.array([np.nan]).astype("i8")
array([9223372036854775807])
 This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. Would https://github.com/pandas-dev/pandas/pull/50183/files also address the issue? Yes, it does.

https://build.opensuse.org/project/monitor/home:Andreas_Schwab:riscv:python thanks @andreas-schwab 