Update test_all_apis (test_pwm_multi_duty)

- in test_pwm_multi_duty,
Increased the N to 5000 because
if N is too small, sometimes the test could fail.

samples/test_all_apis.cpp

@@ -564,14 +564,16 @@ class APITests
 
             GPIO::PWM p(pin_data.out_a, 500);
             p.start(pct);
-            constexpr int N = 1000;
+            constexpr int N = 5000;
             for (int i = 0; i < N; i++)
                 count += GPIO::input(pin_data.in_a);
 
             p.stop();
 
-            auto min_ct = 10 * (pct - 5);
-            auto max_ct = 10 * (pct + 5);
+            const auto weight = N / 100.0;
+            const auto delta = 5;
+            const auto min_ct = weight * (pct - delta);
+            const auto max_ct = weight * (pct + delta);
 
             assert(min_ct <= count && count <= max_ct);
             GPIO::cleanup();