Fix key name for MessageRegistry

Message registry stores messages in the Messages property.
The generator uses the Message property instead. Fix this.

See the spec [1]

And other registries [2] and [3].

[1] https://redfish.dmtf.org/schemas/v1/MessageRegistry.v1_6_3.json
[2] https://raw.githubusercontent.com/openbmc/bmcweb/refs/heads/master/redfish-core/include/registries/openbmc.json
[2] https://redfish.dmtf.org/registries/Environmental.1.1.0.json

Change-Id: I3f8073f1b5c8085059d0335cc7ff3625cd26f756
Signed-off-by: Igor Kanyuka <ifelmail@gmail.com>
diff --git a/tools/sdbusplus/event.py b/tools/sdbusplus/event.py
index 66bcdb5..0dedefb 100644
--- a/tools/sdbusplus/event.py
+++ b/tools/sdbusplus/event.py
@@ -224,7 +224,7 @@
             "@odata.type": "#MessageRegistry.v1_6_3.MessageRegistry",
             "Id": f"{registryName}.{self.version}",
             "Language": f"{language}",
-            "Message": messages,
+            "Messages": messages,
             "Name": f"OpenBMC Message Registry for {self.name}",
             "OwningEntity": "OpenBMC",
             "RegistryPrefix": f"{registryName}",