Update location of boot::signal_event in changelog

Author: nicholasbishop

uefi/CHANGELOG.md

@@ -1,5 +1,8 @@
 # uefi - [Unreleased]
 
+## Added
+- Added `boot::signal_event`.
+
 ## Changed
 - **Breaking:** Removed `BootPolicyError` as `BootPolicy` construction is no
   longer fallible. `BootPolicy` now tightly integrates the new `Boolean` type
@@ -10,7 +13,6 @@
 - `SimpleNetwork::transmit` now passes the correct buffer size argument.
   Previously it incorrectly added the header size to the buffer length, which
   could cause the firmware to read past the end of the buffer.
-- `boot::signal_event()` is implemented.
 
 
 # uefi - 0.34.1 (2025-02-07)