ci(legacy_pcnt): re_enable legacy_pcnt test on c5

docs/en/api-reference/peripherals/pcnt.rst

@@ -163,6 +163,8 @@ It is recommended to remove the unused watch point by :cpp:func:`pcnt_unit_remov
 
         When a watch step and a watch point are triggered at the same time (i.e. at the same absolute point), the callback function only gets called by once.
 
+        The step increment will be reset to 0 when the count reaches the high/low limit value. Please do not rely too much on the exact step interval.
+
     .. code:: c
 
         // add positive direction watch step with 100 step intervals

docs/zh_CN/api-reference/peripherals/pcnt.rst

@@ -163,6 +163,8 @@ PCNT 单元可被设置为观察几个特定的数值，这些被观察的数值
 
         当观察步进和观察点同时被触发时，回调函数只会被调用一次。
 
+        当计数达到上/下限值时，步进增量会被重置为 0，请勿过分依赖于精确的步进间隔。
+
     .. code:: c
 
         // add positive direction step notify with 100 step intervals