esp_adc: increase adc continuous iram test time overhead a bit

Prior to this commit, overhead is 0us on esp32s2, s3, c3, c2. However
when the conv_done event happens, software takes some time to do
necessary operations.

components/driver/test_apps/legacy_adc_driver/main/test_app_main.c

@@ -8,7 +8,7 @@
 #include "unity_test_runner.h"
 #include "esp_heap_caps.h"
 
-#define TEST_MEMORY_LEAK_THRESHOLD (-300)
+#define TEST_MEMORY_LEAK_THRESHOLD (-400)
 
 static size_t before_free_8bit;
 static size_t before_free_32bit;

components/esp_adc/test_apps/adc/main/test_adc_driver_iram.c

@@ -219,7 +219,7 @@ TEST_CASE("ADC continuous work with ISR and Flash", "[adc_oneshot]")
     //This may need to be bigger, when the sampling freq is low
     uint32_t overhead_us = 150;
 #else
-    uint32_t overhead_us = 0;
+    uint32_t overhead_us = 50;
 #endif
     uint32_t wait_time_us = (1000 * 1000 / ADC_TEST_FREQ_HZ * ADC_TEST_PKG_SIZE / SOC_ADC_DIGI_RESULT_BYTES) + overhead_us;
     printf("period is %d us\n", wait_time_us);