Add PyO3 iterator fix references

[cookesan]

Adds the upstream merge commit and fixed release reference for the PyO3 list and tuple iterator advisory.

Evidence checked:

• fix bugs with list / tuple iterator "nth" operations PyO3/pyo3#6086 is merged as 3d48a540572a86548a8f670ea96fa486036d476a.
• v0.29.0 contains that merge commit and lists the iterator security fix.
• crates.io pyo3 0.29.0 matches the registry checksum and contains the checked iterator arithmetic plus large-skip regression coverage; pyo3 0.28.0 has the unchecked target-index math in the affected iterator code.

[cookesan]

Closing as a duplicate of #8234.