Apply suggestions from code review

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

data/event-schemas/schema/m.room.message$m.key.verification.request.yaml

@@ -11,7 +11,7 @@ properties:
       body:
         type: string
         description: |-
-          a fallback message to alert users that their client does not support
+          A fallback message to alert users that their client does not support
           the key verification framework, and that they should use a different method
           to verify keys.  For example, "Alice is requesting to verify keys with you.
           However, your client does not support this method, so you will need to use
@@ -58,6 +58,7 @@ properties:
       - from_device
       - methods
       - msgtype
+      - to
     type: object
   type:
     enum: