autotests: Fix stuck A key in testInputMethod

There's a press event but no matching release event.


(cherry picked from commit de48120c2a)

Co-authored-by: Vlad Zahorodnii <vlad.zahorodnii@kde.org>

autotests/integration/inputmethod_test.cpp

@@ -664,6 +664,8 @@ void InputMethodTest::testModifierForwarding()
     shellSurface.reset();
     QVERIFY(Test::waitForWindowClosed(window));
     QVERIFY(!kwinApp()->inputMethod()->isActive());
+
+    Test::keyboardKeyReleased(KEY_A, timestamp++);
 }
 
 void InputMethodTest::testFakeEventFallback()