fix(webSocket): return the correct type for WebSocketSubject multiplex method(#6232)

* chore: update type for multiplex operator

* chore: update api_guard for websocket

Author: Pernett98

api_guard/dist/types/webSocket/index.d.ts

@@ -3,7 +3,7 @@ export declare function webSocket<T>(urlConfigOrSource: string | WebSocketSubjec
 export declare class WebSocketSubject<T> extends AnonymousSubject<T> {
     constructor(urlConfigOrSource: string | WebSocketSubjectConfig<T> | Observable<T>, destination?: Observer<T>);
     lift<R>(operator: Operator<T, R>): WebSocketSubject<R>;
-    multiplex(subMsg: () => any, unsubMsg: () => any, messageFilter: (value: T) => boolean): Observable<any>;
+    multiplex(subMsg: () => any, unsubMsg: () => any, messageFilter: (value: T) => boolean): Observable<T>;
     unsubscribe(): void;
 }
 

src/internal/observable/dom/WebSocketSubject.ts

@@ -222,7 +222,7 @@ export class WebSocketSubject<T> extends AnonymousSubject<T> {
    */
   multiplex(subMsg: () => any, unsubMsg: () => any, messageFilter: (value: T) => boolean) {
     const self = this;
-    return new Observable((observer: Observer<any>) => {
+    return new Observable((observer: Observer<T>) => {
       try {
         self.next(subMsg());
       } catch (err) {