PYSEC-2023-121 is missing a fix range

[woodruffw]

I think this is a data quality issue. TL;DR:

• PYSEC-2023-121 and GHSA-5c9c-6x87-f9vm are aliases of one another
• PYSEC-2023-121 has no fix, but GHSA-5c9c-6x87-f9vm does (>= 1.5.4)

Ref: https://osv.dev/vulnerability/GHSA-5c9c-6x87-f9vm

I can look into a data tweak for the above.

[woodruffw]

#250 also observes that this might not need a PYSEC advisory at all, since it doesn't affect the zstd Python package (only the zstd CLI).