Visual test: consistent baseline with no randomization (#17380)

frontend/test/metabase-visual/onboarding/urls.cy.spec.js

@@ -8,7 +8,13 @@ describe("visual tests > onboarding > URLs", () => {
 
   it("home", () => {
     cy.intercept("GET", `/api/automagic-dashboards`).as("automagic-dashboards");
-    cy.visit("/");
+
+    cy.visit("/", {
+      // to give predictable messages based on randomization
+      onBeforeLoad(win) {
+        cy.stub(win.Math, "random").returns(0.42);
+      },
+    });
 
     cy.wait("@automagic-dashboards");