Update changelogs from fern repo (#541)

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

Author: fern-support

fern/products/sdks/overview/ruby/changelog/2025-08-20.mdx

@@ -1,3 +1,6 @@
+## 1.0.0-rc12
+**`(fix):`** Support multipart form uploads.
+
 ## 1.0.0-rc11
 **`(fix):`** Install dependencies after generating the SDK to produce a Gemfile.lock.