fix mnemonic test

Signed-off-by: tobiasKaminsky <tobias@kaminsky.me>

src/androidTest/java/com/nextcloud/client/SettingsActivityIT.java

@@ -65,6 +65,8 @@ public class SettingsActivityIT extends AbstractIT {
     public void showMnemonic_Error() {
         SettingsActivity sut = activityRule.launchActivity(null);
         sut.handleMnemonicRequest(null);
+        shortSleep();
+        waitForIdleSync();
 
         screenshot(sut);
     }