Stub out calls to vector.im and matrix.org in Cypress (#9652)

cypress/e2e/login/login.spec.ts

@@ -21,6 +21,10 @@ import { SynapseInstance } from "../../plugins/synapsedocker";
 describe("Login", () => {
     let synapse: SynapseInstance;
 
+    beforeEach(() => {
+        cy.stubDefaultServer();
+    });
+
     afterEach(() => {
         cy.stopSynapse(synapse);
     });

cypress/e2e/register/register.spec.ts

@@ -22,6 +22,7 @@ describe("Registration", () => {
     let synapse: SynapseInstance;
 
     beforeEach(() => {
+        cy.stubDefaultServer();
         cy.visit("/#/register");
         cy.startSynapse("consent").then(data => {
             synapse = data;