Check state key while parsing m.call.member state events.

[toger5]

Currently we do not check m.call.member state event keys allowing users to have multiple events for one device.

This is not to spec.
We should check the key when parsing the state event here:

matrix-js-sdk/src/matrixrtc/CallMembership.ts

Lines 45 to 63 in 8ebf04a

	if (!(data.expires || data.expires_ts)) {
	throw new Error("Malformed membership: expires_ts or expires must be present");
	}
	if (data.expires) {
	if (typeof data.expires !== "number") {
	throw new Error("Malformed membership: expires must be numeric");
	}
	}
	if (data.expires_ts) {
	if (typeof data.expires_ts !== "number") {
	throw new Error("Malformed membership: expires_ts must be numeric");
	}
	}
	if (typeof data.device_id !== "string") throw new Error("Malformed membership event: device_id must be string");
	if (typeof data.call_id !== "string") throw new Error("Malformed membership event: call_id must be string");
	if (typeof data.scope !== "string") throw new Error("Malformed membership event: scope must be string");
	if (!parentEvent.getSender()) throw new Error("Invalid parent event: sender is null");
	}

Comment with more details: #4262 (comment)