[QA]Change screenshot size for metricbeat dashboard test (elastic#199378

)

## Summary

Change the default screenshot compare size for the metricbeat dashboard.

(cherry picked from commit c5df736)

x-pack/test/stack_functional_integration/apps/metricbeat/_metricbeat_dashboard.ts

@@ -55,7 +55,7 @@ export default function ({
       await PageObjects.common.dismissBanner();
       await PageObjects.dashboard.waitForRenderComplete();
       await PageObjects.common.sleep(2000);
-      await browser.setScreenshotSize(1000, 1937);
+      await browser.setScreenshotSize(1400, 1937);
       await PageObjects.common.sleep(2000);
     });