tests: benchmarks: multicore: idle_spim_loopback: Add boot delay

Pytest requires the first captured state to be low power state.
Due to internal test framework delays, Pytest collects last ~27 ms
of the idle state. Then MCU wakes up. As a result some Idle tests
started to randomly fail.

Add arbitrary delay at the beginning of main so the first wake up
happens later.

Signed-off-by: Sebastian Głąb <[email protected]>

Author: nordic-segl

tests/benchmarks/multicore/idle_spim_loopback/src/main.c

@@ -166,6 +166,9 @@ int main(void)
 #endif
 	LOG_INF("===================================================================");
 
+	/* Arbitrary sleep to fix CI synchronization. */
+	k_msleep(100);
+
 	ret = spi_is_ready_dt(&spim_spec);
 	if (!ret) {
 		LOG_ERR("Error: SPI device is not ready");