sdbus++: events: schema: explicitly prohibit unspecified properties

Modify the schema so that properties that do not belong are called
out as a schema violation.  It was easy for someone to accidentally
add 'severity' on events, which should only be specified on errors.
Adding it to the schema to prohibit makes it clearer what the
expectations are.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I3decce5cddce2ce7215f7351339157a2597fdb0b
diff --git a/tools/sdbusplus/schemas/events.schema.yaml b/tools/sdbusplus/schemas/events.schema.yaml
index 26e8816..1ee280b 100644
--- a/tools/sdbusplus/schemas/events.schema.yaml
+++ b/tools/sdbusplus/schemas/events.schema.yaml
@@ -58,9 +58,14 @@
             - oneOf:
                   - $ref: "#/$defs/redfish-messages"
                   - $ref: "#/$defs/redfish-map"
+        unevaluatedProperties: false
     error:
         type: object
-        $ref: "#/$defs/event"
+        allOf:
+            - $ref: "#/$defs/base-event"
+            - oneOf:
+                  - $ref: "#/$defs/redfish-messages"
+                  - $ref: "#/$defs/redfish-map"
         properties:
             severity:
                 enum:
@@ -80,6 +85,7 @@
         required:
             - severity
             - errno
+        unevaluatedProperties: false
     redfish-messages:
         type: object
         properties: