test(browser): leave no state behind for the next case

Await the form's explicit unmount: an unmount left running overlaps the
next render's act, and React then commits nothing for the rest of the
file. Return to the newest history entry after stepping back, so the
next case's push adds an entry instead of replacing the forward one.

src/components/measurements/__tests__/measurement-form.browser.test.tsx

@@ -289,7 +289,10 @@ describe("<MeasurementForm> type", () => {
     await first.screen.getByLabelText("Value (kg)").fill("80");
     await first.save.click();
     await expect.poll(() => first.onSuccess.mock.calls.length).toBe(1);
-    first.screen.unmount();
+    // Awaited: the unmount runs inside `act`, and one left running overlaps
+    // the next render's `act`, after which React commits nothing for the
+    // rest of the file (every later case finds an empty container).
+    await first.screen.unmount();
 
     const { screen } = await mount();
     await expect