Clarify that via is required for m.space.parent and m.space.child as per MSC1772. (#1618)

data/event-schemas/schema/m.space.child.yaml

@@ -34,6 +34,8 @@ properties:
           Optional (default `false`) flag to denote whether the child is "suggested" or of interest
           to members of the space. This is primarily intended as a rendering hint for clients to
           display the room differently, such as eagerly rendering them in the room list.
+    required:
+      - via
     type: object
   state_key:
     description: The child room ID being described.

data/event-schemas/schema/m.space.parent.yaml

@@ -20,6 +20,8 @@ properties:
 
           When multiple `canonical` parents are found, the lowest parent when ordering by room ID
           lexicographically by Unicode code-points should be used.
+    required:
+      - via
     type: object
   state_key:
     description: The parent room ID.