CI test failure in `parse_timedelta` (got `str` that cannot be coerced to `float`)

[jakirkham]

s = '1-5.888938903808594e-05', default = 'seconds'
1864

1865
    def parse_timedelta(s, default="seconds"):
1866
        """Parse timedelta string to number of seconds
1867
    
1868
        Examples
1869
        --------
1870
        >>> from datetime import timedelta
1871
        >>> from dask.utils import parse_timedelta
1872
        >>> parse_timedelta('3s')
1873
        3
1874
        >>> parse_timedelta('3.5 seconds')
1875
        3.5
1876
        >>> parse_timedelta('300ms')
1877
        0.3
1878
        >>> parse_timedelta(timedelta(seconds=3))  # also supports timedeltas
1879
        3
1880
        """
1881
        if s is None:
1882
            return None
1883
        if isinstance(s, timedelta):
1884
            s = s.total_seconds()
1885
            return int(s) if int(s) == s else s
1886
        if isinstance(s, Number):
1887
            s = str(s)
1888
        s = s.replace(" ", "")
1889
        if not s[0].isdigit():
1890
            s = "1" + s
1891
    
1892
        for i in range(len(s) - 1, -1, -1):
1893
            if not s[i].isalpha():
1894
                break
1895
        index = i + 1
1896
    
1897
        prefix = s[:index]
1898
        suffix = s[index:] or default
1899
    
1900
>       n = float(prefix)
1901
E       ValueError: could not convert string to float: '1-5.888938903808594e-05'
1902

1903
../../../miniconda3/envs/dask-distributed/lib/python3.8/site-packages/dask/utils.py:1468: ValueError

https://github.com/dask/distributed/runs/2088606636

[jrbourbeau]

This error also appeared in a different test, distributed/tests/test_client_executor.py::test_map, over in #4563 (see this CI build)