doc: release note for changed {sign,verify}message error codes

Author: theStack

doc/release-notes-18466.md

@@ -0,0 +1,10 @@
+Low-level RPC changes
+---------------------
+
+- Error codes have been updated to be more accurate for the following error cases (#18466):
+  - `signmessage` now returns RPC_INVALID_ADDRESS_OR_KEY (-5) if the
+    passed address is invalid. Previously returned RPC_TYPE_ERROR (-3).
+  - `verifymessage` now returns RPC_INVALID_ADDRESS_OR_KEY (-5) if the
+    passed address is invalid. Previously returned RPC_TYPE_ERROR (-3).
+  - `verifymessage` now returns RPC_TYPE_ERROR (-3) if the passed signature
+    is malformed. Previously returned RPC_INVALID_ADDRESS_OR_KEY (-5).