search_sorted does not handle series sorted with nulls_last=True

[nameexhaustion]

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

Reproducible example

pl.Series([2, 2, None], dtype=pl.Int8).search_sorted(1, side="left")
# outputs 0 (correct)
pl.Series([2, None, None], dtype=pl.Int8).search_sorted(1, side="left")
# outputs 3 (incorrect)

Log output

No response

Issue description

Expected behavior

assert pl.Series([2, None, None], dtype=pl.Int8).search_sorted(1, side="left") == 0

Installed versions

0.20.15

[orlp]

This was fixed in #16447.