Fix TestKeyboardPress panic

This only fixes the panic, but not the underlying error with
WaitForEvent. There is clearly an issue with WaitForEvent as we can
also see in #1506.

tests/keyboard_test.go

@@ -138,7 +138,7 @@ func TestKeyboardPress(t *testing.T) {
 				return nil
 			},
 		)
-		assert.NoError(t, err)
+		require.NoError(t, err)
 
 		// Wait for the new tab to complete loading.
 		assert.NoError(t, newTab.WaitForLoadState("load", nil))