Inappropriate result of expr skew and kurtosis for a magic constant inputs

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[X] I have checked that this issue has not already been reported.
[X] I have confirmed this bug exists on the latest version of Polars.

Reproducible example

import polars as pl
a = pl.DataFrame({"a": [1.0042855193121334] * 60})
for l in range(60):
     print(l, a.slice(0, l).select(pl.col('a').kurtosis()).item())

output

Log output

I did not obtain log here.

Issue description

expect to constantly get nan for any size, but get None when size is 0 and -2 when size >= 22

Expected behavior

import polars as pl
a = pl.DataFrame({"a": [1.0042855193121334] * 60})
for l in range(60):
      print(l, st.kurtosis(a.slice(0, l).select(pl.col('a')).to_numpy().flatten()))

get nan consistently

Installed versions

``` --------Version info--------- Polars: 1.5.0 Index type: UInt32 Platform: Linux-3.10.107-1-tlinux2_kvm_guest-0056-x86_64-with-glibc2.28 Python: 3.9.9 (main, Apr 24 2023, 09:37:21) [GCC 10.2.0] ----Optional dependencies---- adbc_driver_manager: cloudpickle: 2.2.1 connectorx: deltalake: fastexcel: fsspec: 2023.4.0 gevent: 22.10.2 great_tables: hvplot: matplotlib: 3.9.2 nest_asyncio: 1.5.6 numpy: 1.24.2 openpyxl: 3.1.2 pandas: 1.5.3 pyarrow: 15.0.2 pydantic: 1.10.18 pyiceberg: sqlalchemy: 2.0.24 torch: 1.11.0+cu102 xlsx2csv: xlsxwriter: ```

pola-rs / polars