Update changelogs from fern repo (#4317)

Author: fern-support

fern/products/cli-api-reference/cli-changelog/2026-03-17.mdx

@@ -0,0 +1,7 @@
+## 4.31.1
+**`(fix):`** Fix `x-fern-streaming` with `stream-condition` emitting the condition field
+as an optional boolean instead of a required literal in split request types.
+When the source property was nullable (`type: [boolean, "null"]`), the spread
+order allowed the original property to overwrite the literal overrides.
+
+