test: refactor a menu test case to have it pass on CI env

For some unknown reason, scroll events were triggered upon mouse wheel, even though scroll
was prevented. It didn't happen when running locally headless with `cypress run`, so it seems like the only differentiating factor is the OS being linux in the CI env.

The test is changed to compare actual scrollY of the window, instead of checking if scroll event handlers are called.

packages/jui/src/Menu/Menu.cy.tsx

@@ -889,51 +889,44 @@ describe("ContextMenu", () => {
   });
 
   it("disables the scroll of the document when the menu is open", () => {
-    const ScrollListener = (props: { onScroll: () => void }) => {
-      React.useEffect(() => {
-        const onScroll = () => {
-          props.onScroll();
-        };
-        document.addEventListener("scroll", onScroll);
-        return () => {
-          document.removeEventListener("scroll", onScroll);
-        };
-      });
-      return null;
-    };
-    const onScroll = cy.stub().as("onScroll");
     cy.mount(
       <>
-        <ScrollListener onScroll={onScroll} />
+        <div style={{ height: "10rem" }} id="element-above" />
         <ContextMenuContainer
           id="container"
-          style={{ margin: "10rem 0", height: "100vh", background: "#aaa" }}
+          style={{
+            height: "100vh",
+            overflow: "auto",
+            background: "#aaa",
+          }}
           renderMenu={() => (
             <Menu aria-label="Test Context Menu">
               <Item>Menu item</Item>
             </Menu>
           )}
         >
-          {" "}
+          scrollable container
+          <div style={{ height: "150vh" }}></div>
         </ContextMenuContainer>
       </>
     );
     cy.get("#container").rightclick("top", {
       scrollBehavior: false,
     });
-    cy.findByRole("menu");
-
-    // onScroll was called in a run of the pipeline on the CI env.
-    // Not sure why but trying to work around the flakiness by a wait.
-    // https://cloud.cypress.io/projects/o1ooqz/runs/255/overview/0aa04a42-1030-4ab6-a8b2-1fe08069a705?roarHideRunsWithDiffGroupsAndTags=1
-    cy.wait(100);
-
-    cy.get("#container").realMouseWheel({
-      deltaY: 5,
-      scrollBehavior: false, //  we don't want cypress to do any extra scrolling
-    });
-    cy.wait(200); // maybe a bug in realMouseWheel, but before the wait, the next command runs before scrolling happens
-    cy.wrap(onScroll).should("not.be.called");
+    cy.window()
+      .its("scrollY")
+      .then((scrollBefore) => {
+        cy.get("#element-above").realMouseWheel({
+          deltaY: 5,
+          scrollBehavior: false, //  we don't want cypress to do any extra scrolling
+        });
+        cy.wait(200); // maybe a bug in realMouseWheel, but before the wait, the next command runs before scrolling happens
+        cy.window()
+          .its("scrollY")
+          .then((scrollAfter) => {
+            expect(scrollAfter).to.eq(scrollBefore);
+          });
+      });
   });
 
   it("disables the scroll when the menu is open", () => {