tests input/gpio_keys: Add missing overlays for native_sim

During the hwmv1->v2 transition, overlays from a base
board were made to be shared with the variants.
So at that time all overlays for variants which were
just copies of the base overlay were removed.
After that in
zephyrproject-rtos/zephyr#71149
this shared/merged overlay behaviour was reverted,
but not all tests were fixed.

This is one of those. Let's fix it.

(cherry picked from commit cf533cc)

Original-Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>
GitOrigin-RevId: cf533cc
Change-Id: I0ef73d67d20ea4a0fbba46808a9bf31713eddfcc
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5465918
Reviewed-by: Jeremy Bettis <jbettis@chromium.org>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Commit-Queue: Jeremy Bettis <jbettis@chromium.org>
Tested-by: Jeremy Bettis <jbettis@chromium.org>

tests/drivers/input/gpio_keys/boards/native_sim_native_64.overlay

@@ -0,0 +1,6 @@
+/*
+ * Copyright (c) 2024 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include "native_sim.overlay"