Update changelogs from fern repo (#718)

Co-authored-by: tjb9dc <[email protected]>

Author: fern-support

fern/products/sdks/overview/python/changelog/2025-09-05.mdx

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+## 4.28.1
+**`(fix):`** Union member self-referencing dependencies are now correctly imported and forward referenced.
+This fixes compatibility with Pydantic >=2.11.0.
+
+