Update changelogs from fern repo (#4936)

Author: fern-support

fern/products/sdks/overview/python/changelog/2026-04-10.mdx

@@ -1,3 +1,7 @@
+## 5.4.0-rc.0
+**`(feat):`** Upgrade to IR v66 which compresses the IR Name type, reducing IR size and increasing performance.
+
+
 ## 5.3.11
 **`(fix):`** Fix duplicate keyword arguments in generated code for discriminated union
 request bodies with stream condition properties. When a union variant inherits